Rockuman said:
This one isn't a particle. It's the copula. It's best thought of in English as the verb "to be," but perhaps more accurately it can be thought of as an equal sign.
Kore da -> "It's this."
Rockuman said:
De is used to show an instrument (
basu de ikimashita -> "I went by bus") or location of some
action (
kouen de asonda -> "We played in the park."). It also has some uses that seem to be an extension of this.
Kore de seems to be most often translated as "now," but it's more like "by means of this." Here's an example:
Kore de daigaku ni ikeru -> "Now I will be able to go to college/university." Note here that literally this is more like "by means of this I can go to college," where "this" is something understood from context, like getting a grant, for instance.
Rockuman said:
Watashi wa & Watashi ga (not sure what the difference is)
Most people have problems with this. For this problem I will refer you to this page about
topics and focuses.
Rockuman said:
And also, I often hear that "ii yo ne" can be translated as "Be prepared" or something similar. I'm not sure how "Good, an emphasis particle, and an agreement" come together to form preparation, but, that's what I'm here for.
Check out the
EXCEED和英辞典 definition of
ii. It can mean "alright" or "enough," as well as "good." I think in the situation you're talking about there is probably an understood subject (perhaps more accurately, an unstated topic),
kakugo. The phrase
kakugo wa ii means to be prepared for some bad fate. Saying
ii yo ne is probably like saying "you're prepared for your fate, aren't you?" I'm not sure I did a good job with that one. We'll find out when some of the more knowledgeable members stop by.