"Wanna", "gonna" and "gotta" (and their sloppy friends) only exist because that's what they sound like - more or less - in slurred or fast speech. They are not real words and they don't function as verbs. For past tense, you still need to conjugate the actual verb (want - wanted; is going to - was going to; get - got). "He wanna" is completely wrong, even in casual speech. You would say something closer to "wansta" (ie. wants to) or "wanidta" (wanted to). Again, remember that there aren't real words. The truth is, when we native English speakers write and speak, we use standard English (want to, going to, have got to). Even if we slur words, we will always repeat the sentence clearly if the other person didn't hear us the first time.

No you should not use "wanna- gotta-gonna" they are not words or contractions of words. You must always use : present tense, past tense: want to , wanted to get to , got to going to , was going to

No, you cannot use these in the past tense because, as you pointed out, they refer to actions performed in the present. It is also important to remember that these words are not actually used in formal writing and so it is not always best to use them unless, of course, you're using them in an informal context.

Thank you Nathan. Have a good evening.

Everyone else has already left some fantastic, helpful comments for you; however, one thing I'd like to note is that 'going to' and 'gonna' implies actions that will take place in the future rather than what's occurring presently.