[steven]

"Thanks for all the advice guys! So you think I should start using 'tamani' when in a sentence, and 'tokidoki' when it's a one-word answer? "

I think that's generally a good idea. That's not to say that "tamani" can't be used in a word-word-answer situation either, though (and it most certainly is used in that way). The point is "tamani" gets way more usage and when "tokidoki" is used, it's mostly in a one-word-answer situation.

"A: Do you go to School? B: Sometimes...
Gakkou ni ikimasu ka. Tokidoki..."

I think there is a negative connotation there-- as in you're supposed to go to school, but you only go "sometimes" (I personally feel that same connotation is present in your English phrasing as well). If that's what you want to say, then it's fine. If you only have to go to school once or twice a week, it might be a good idea to put that in there just so you don't come off as a "slacker" (excuse my lack of a better term) when you don't want to.

"Another point: I was having a bit of trouble using wa and ga in sentences. "
If we're talking about spoken Japanese, you don't really have to have は. Even if you have the subject, you still don't have to have は. There are alternatives as well (like って and stuff like that).

"(Ignoring the fact that 'watashi wa' is rarely used in day to day language. In fact, this kind illustrates why it isn't? You wouldn't say 'about me' in every of your sentences in English either. Ok, the logic isnt perfect, but it works for me...>.>)"
It is my opinion that you are trying to compare Japanese to English too much. I think doing so will cause a lot of confusion (from the basics to the advanced). Somethings just don't make sense in one language even though they make perfect sense in another.

As for this example:
"Watashi ga Yuko desu.
'It is me who is Yuko'"

I'm not so sure about this... I think you generally should just stick to 私は～（名前）.

As far as 私が～ goes, you could use it like this:
私が勝った犬 (the dog that I owned)
私が好きなサンドイッチ (the sandwich that I like)
私が好きだったアイスクリーム (the ice cream that I liked)

The subject in those cases would not be "I/私", but they would be whatever "I/私" is modifying. So if you have something like "私が勝った犬" it would be followed by an action or an adjective or soemthing like that.
ie: "私が勝った犬って可愛かった" (The dog I owned was cute)
ie: "私が好きなサンドイッチは売り切れちゃった” (the sandwhich I like got sold out)
etc.

That's how I look at it anyways... I mean in some situations you need it and sometimes you don't. For example "私が勝った犬って可愛かった” could just as easily be said as "俺の犬可愛かったな” (my dog sure was cute [or something to that effect]).

I hope that clears things up. I don't know if I did a good job explaining it though.