well,you cant really be thought to wheelie...its one of those things where you need to be confident in urself and have the balls not to be afraid to wreck...ive been stunting since i was 14...im 26 now...
but to answer ur questions...
1. Throttle depends on ur bike,none are the same and all react diffrent.
2. Normally 2nd gear bc its a longer gear and you can practice threw that for a while till you have that down
3. Balance,thats allllll on you and ur control,like i said all bikes are diff,and so are rider weight.
i know it doesnt help much but that basically all i can help u with bro.