I would recommend a cnotch on a 2/4 although not required. I would definitely say it’s required on 3/5 or lower. I would also recommend just doing it once and going straight for the 4/6. I started at 2/2 and now I’m on about 5/8 and wishing it was lower.So on a 3/5 kit is a C-NOTH absolutely needed.
I think I'm gonna go with the 3/5 first to see if I like it then 4/6 if not low enough...I know with a 6 you gotta c notch