i feel like i am stuck at the moment because i use my right hand too much, im trying to learn to fully alternate as many 3 notes long pattern as possible but it is hard. also should i try to not use only one hand when playing the slower parts of a song?

very important. actually a lot of top kddk players started with singletap, then they started doing alterantes. usually they still do 1/1 snap singletaps during high bpms. the rest is alternate.

how to learn it is just to try to do it not too hard, start slow. good luck

not true, play how you want.
singletapping 1/2 is viable all the way up to like 340, rolling is viable to an insane rank, almost any playstyle can work.
if you want to alternate a pattern because you think it makes it more comfortable/easier to play/"better technique", go ahead! if you want to singletap higher BPMs because you find alternating a bit too much, also go ahead!
play the way that makes sense to you and don't let anyone tell you what's wrong and what's right