if just based on merit: i think vegeta is the better unit because he has more defense then hit, but if you have a USS team hit might be better because he links well with jiren and that is a deadly rotation.
in short i'd say go with hit for USS or vegeta because of his super class sub lead
i'd say swap out teq cell for the LR cell he can do some nice damage on this team. i dunno how good android 21 will work i know she can hit hard as well. my only problem with kid buu is he has zero ki links so he almost always has to be on rotation with rose in order to recieve a super most of the time, so if that bothers you might consider swapping him out as well
they shine well on an androids team and overall they do around 1m damage on average so pretty good, normally i run str final form frieza but i was doing sbr and needed an agl unit, decided to try them over super 17
aside from leveling up, there are items in the baba shop that do it i believe, but leveling up is definitely the best way but not always the fastest,im at rank 365 so i have alot of team cost. but i think most teams can be run by rank 150? im not entirely sure but you have nice teams even with low cost
ayyy congrats on lr gogeta, an amazing unit. as for getting kais, there are story missions and exchanging the items for kais, there super battleroad (dont recommend its pretty hard). and that android isn't that good so i wouldn't worry about using him, your team is better without
it couldn't hurt, i'd say if you can complete it do kid buu's EZA and use the 30 stones from that to do a multi to try and grab her if you really want to. otherwise save for gogeta and broly as they will be out next month