Did you try resetting your ui? Lots of issues dealing with your display/ui/numbers are solved with that.

Sentinel/Marauder are probably the hardest to be good at in my opinion. So stay away from those, their rotations are ridiculous and you have to watch 6-10 abilities constantly as to know when they're off cooldown. Easiest, probably BH/Tr if you know how to manage resources.

Best sniper stream available.