I personally would have gone for variant 4 completion to get some hands on rank up gems. Then act 5 completion. Unless you are a highly skilled player, you are not ready to enter cavalier atm. You don't have any counters as well. V4 completion looks like the best bet.
from 5.3- end of act 5 your roster can for sure take on that classic ultron, I reccomend using Corvus or a ramped g2099 for him. In terms of act 6 you could probably do 6.1 but it may take some revives depending on your skill and rank up hyperion for that xbones and sentinel bosses, he will help a bunch.
Guys I have been uncollected for some time now and am thinking of going to cavalier. Below is my roster. Need rank up advice and any specific counters or any nodes? Should I explore act 4 first??