Goku can go up to Super Saiyan 4 there is no DB AF.
yes he can transfom into 3 levels of super saiyan but the forth is a seperate character
Goku SSJ4 is the most powerful super saiyan form that Goku can transform into
No super saiyan 4 is the max Goku can transform too.
Gohan is stronger if goku is in his normal form but if they are both in super saiyan 2 form or if Goku is in super saiyan form then goku is stronger.
4
In the fictional TV series Dragon Ball, and all its successors, it is possible for a normal human to become a Super Saiyan by use of a Dragon Ball wish. Otherwise, according to Goku, a Saiyan unlocks the Super Saiyan transformation in a time of great need. However, Vegeta became a Super Saiyan just by desperately wanting to surpass Goku.
When he was in the Hyperbolic Time Chamber training to beat Cell. I think he became Super Saiyan 2 after he died to save the world from Cell. If Goku could turn Super Saiyan 2 he would have beaten Cell himself, instead of making ohan fight him.
Gogeta, the fusion of super saiyan 4 Goku and Vegeta.
Super Saiyan 2 goku cause he was able to defeat Broly as a Super Saiyan 1
Goku does not turn super saiyan 6 or 5 in fact. and it only goes up to super saiyan 3 in the manga and super saiyan 4 in the cartoon.
Yes each super saiyan stage is stronger than the previous for example super saiyan 2 goku is stronger than super saiyan goku although the second stage is slower than the first stage power wise it's an improvement super siayan 3 is stronger than 2 and faster as well super saiyan 4 goku is the fastest super saiyan form (of goku only not counting fusion with vegeta) and is the last duper saiyan stage goku reaches.
No one is stronger than Goku in the beginning(other than raditz,vegeta,knappa) when Goku was on break) but when vegeta becomes the pure of heart the transision does not allow him to transform to super saiyan 3, but with machine, he can become super saiyan 4, and his switch to good makes him the same strength, if not stronger than Goku