They show Goten going Super Sayin first when he first trained with Gohan. However, Goten actually was able to go Super Sayin way before that and even showed his mom but they don't show that although...
Of course not, that is way to much power for a 6 year old to obtain.
no but there are some drawings of he and trunks in ss2 and ss4
episode 206
Yeah it is in Dragon Ball GT.