えてして見掛け倒し is not a set phrase.
見掛け倒し means to give false impression, i.e. it is weaker/less powerful/not so good as it looks.
If one says XXX is えてして見掛け倒し, it means "XXX tends to be less (you can name any adjective meaning good) than it looks".
なにぶん - its meaning varies depending on the context.
It is equivalent to douzo or douka when used with yoroshiku onegaishimasu (according to dictionary) but for me such a usage is rare.
It is often used as a kind of pretext for an excuse. Maybe close to "that said"? I'm not sure...
e.g.
なにぶん子どものことですから、許してやってください
But he's only a child, so please let it pass.
ういっす -
Indeed it 'developped' from "good morning", and yes, it is used mostly by males. Some young girls might use it among friends but not common.
あいにく - the dictionary gives several usages, including "unfortunately". In Japanese, how does one express the idea of "fortunately" and "unfortunately"? My guess is that "fortunately is "幸運にも"、and unfortunately to be あいにく、 or 残念ながら, but I am not 100% sure. I don't want it to sound very katai in conversation though
There are many expression to show one's regret, sorrow, etc. and opposite.
Unfortunately
あいにく and 残念ながら are very common. If you want to sound more casual, how about 残念だけど?
Fortunately
幸運にも and ありがたいことに are the words that came to my mind.
There could be many other words, you may want to hear other's comments.
よかた - I cannot think of a words/phrase that sounds like this and have meaning "face"... sorry. Face as in saving face is 面目(めんもく) but it sounds quite different. (Surely it is not よかった?)
ここ数年
It is possible to say この数年, but ここ数年 is also correct.
ここ does not refer to the closeness of only the space but in timespan as well.
ここ数日、ここ2、3年、ここ何週間か etc. are commonly used.
There's a similar expression which sounds like to indicate a place, but actually time: このところ (these days)
Maybe a "full version" of ~とばかりに is ~といわんばかりに (as if to say/to iuyou ni). It's rather old way of expression, it can be used in conversation but more used in writing, as you guessed.
Hope the above helps a bit.