Duolingo Japanese Course-Related Questions

I've started this thread as a place to ask questions related to Duolingo's course for learning English from Japanese. I'm using this course to learn Japanese, since there is not currently a English-Japanese course. If anyone else who is using the Duolingo course to learn Japanese want's to ask a question related to it, then fell free to do so here.
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As for my first question, I've come to a problem that asks me to translate 'Are we men?' into Japanese. I translated it as
「私達は男たちですか。」, which was marked as correct, but another answer labeled as correct was listed:
「私たちは男の人ですか？」
I have a few questions about these. First, is there any difference between 達 & たち as a pluralising suffix?
Second, I noticed that in the Duolingo translation they kept 男の人 singular instead of pluralising it. Is there any particular rule as for when you should pluralise a noun?

EDIT: I've just come across the sentence 「あなたは牛乳を飲む。」. I was wondering when you should keep the verb in its basic form and when you should change it to its ~masu form （飲む ｖｓ． 飲みます）

EDIT 2: I've encountered a problem that asks for a translation of 'They have a newspaper'. The listed translation is 「彼らは新聞を持っている。」. I would like to know why the present progressive form was used instead of the ~masu form. I put 「彼らは新聞を持ちます。」 and it was marked as incorrect.
(Since Duolingo presents a relatively large number of sentences in a short period of time, I may have a fair number of additional questions between answers.)

EDIT 3: I've just come across this sentence: 「いや、違う、そうじゃない！」, which Duolingo translates as 'No, no, no!'. I really don't know where to begin on this one; I'll probably need a sentence break-down to understand it.

(If you are able to answer any of these questions, then please do. While some people may be able to, I don't necessarily expect any one person to answer all these questions.)

Are you sure this approach is working? It would seem like you're making guesses about the Japanese grammar based on the presented English equivalent. Wouldn't it be better to use a dedicated Japanese learning course/textbook which explains the Japanese grammar in detail? Things like the difference between the plain form vs. the polite (-masu) form, or the meanings of the progressive form, are quite basic things that are explained well in dedicated courses; at this rate you'll have a lot of questions indeed

lanthas said:

Are you sure this approach is working? It would seem like you're making guesses about the Japanese grammar based on the presented English equivalent. Wouldn't it be better to use a dedicated Japanese learning course/textbook which explains the Japanese grammar in detail? Things like the difference between the plain form vs. the polite (-masu) form, or the meanings of the progressive form, are quite basic things that are explained well in dedicated courses; at this rate you'll have a lot of questions indeed

Click to expand...

That question was poorly worded; I have a basic understanding of when to use plain and polite forms.
I was thinking more along the lines of 'Why would Duolingo use the plain form in that example?', though on further reflection, it is probably to illustrate that the translation is the same whether plain or polite form is used.
Also, I have no budget for Japanese learning resources, so I am limited to free online resources and what I can pick up at my local library.
The benefits that I've been gaining from Duolingo (these questions represent a relatively small portion of the things I've come across and learned from on Duolingo) are, in addition to learning vocabulary & grammar, that I am forced to learn the readings of Kanji so that I can type them, I learn to easily recognise the Kanji so that I can provide the English translations, and I learn sentence structure and particles. I learn all these things simultaneously because if I don't, I won't be able to advance. This, in a way, simulates learning by immersion, but at a slower pace, where I can stop and study external resources to catch up if necessary.
If you have any recommendations for any online resources or books that my library may have or be able to purchase, then I'll be completely open to your suggestions. I have tried some free online courses, but some start by teaching me random words, with nothing to help me remember them, while others may teach me the rules without any link to actual usage, making them difficult to remember and apply.

(Also, I've learned Spanish largely by reading and writing examples, and seeking clarification and expansion when I didn't understand a concept.)

You're going to run into issues with the grammar and structure of Japanese being much further from English than Spanish is, so the same methods that worked for Spanish may not work as well for Japanese. In particular, if you haven't been taught how to use a grammar structure first, trying to get you to translate direct from English is unlikely to work out well. Look for material that teaches you the grammar first, then gets you to form lots of sentences with it for practice. Erin's Challenge is I think the best of the online resources. The people who run it also run the JLPT, and there's lots of examples (video skits, manga, etc) alongside the explanations.

Okay, a quick run through your questions:
達 & たち are the same - 達 is just the kanji form. Many times the choice is simply that - a preference. People try to get a nice balance between kanji and kana - a lot of kana with little kanji is more casual and can look childish (since children don't know as many kanji), whereas over-use of kanji can look stiff and old-fashioned. But there is a lot of room for personal preference between the two extremes.

たち is not really a "pluraliser" in the same way as we pluralise in English. It's more of a "grouper". For this reason, you don't normally append it to objects unless you're being poetic (so オレンジたち would be weird, 星たち you might see in fiction or song lyrics or something). Similarly, you can use it attached to names to mean "so-and-so's group", e.g: 田中たち doesn't mean "multiple Tanakas", it means "Tanaka and others". e.g. if Tanaka and some others are going to come to the party together, you might use 田中たち to refer to that particular group of people.

Use たち then not when you mean plural, but when you're identifying a particular grouping of people. So they shouldn't have marked 私達は男たちですか as correct.

In Japanese, context is used to differentiate plural and non-plural.
e.g. 大学生 would mean university student or students, depending on the context.
彼は大学生です。 = student, since 彼 refers to a single person.
私たちは大学生です。 = students, since 私たち refers to multiple people.
大学生は金がないです。 = students, since we're making a general statement about them.
数人の大学生 = students, since we've appended "a few".
一人の大学生 = student, since we've specified there's only one

On your others:
"masu" form is politer. Which form you use depends on who you're speaking to. A very general rule would be plain form for friends, desu/masu (also called 丁寧語/teineigo) for people you don't know well or those senior to you. There are more levels of polite language (keigo), but you really don't need to worry about those for now.

~ている or ~ています, is used for either an ongoing action (I am eating), or a state (I am married). If someone currently has a newspaper, therefore, you should use this form. The plain verb form is used for future (I will get married) or habitual (I eat breakfast at 7am every day). 彼ら is also weird here unless a group of people have one newspaper? Is that not just the gender neutral "they" in English?

いや、違う、そうじゃない！
いや = "no"
違う = literally "different", but used as an assertion to mean "the thing you just said is not correct".
そうじゃない = "it is not like that".

So not "no" as in response "Do you want some coffee?" but "no" as in response to "Are you secretly in love with Tanaka?"

Anybody who can afford an internet connection and a device to connect with can scrape together a few bucks for a decent textbook if they want to. It is just a matter of skipping a few trips to Starbucks with your friends.

I doubt if the people who plead poverty for not buying a textbook have even checked to see how much a textbook costs.

Getting started by learning the basics from a proven textbook is the most economical and efficient use one can make of their time and resources.

Mike Cash said:

Anybody who can afford an internet connection and a device to connect with can scrape together a few bucks for a decent textbook if they want to. It is just a matter of skipping a few trips to Starbucks with your friends.

I doubt if the people who plead poverty for not buying a textbook have even checked to see how much a textbook costs.

Getting started by learning the basics from a proven textbook is the most economical and efficient use one can make of their time and resources.

Click to expand...

Amazon is an excellent resource toward this end.

I agree with Mike; although free is good, more often than not you get what you pay for.