champs I'd upgrade atleast to 5star after Elhain
High Katun, Deepheart
the other champs I wouldnt take any further if I were you atleast not atm (you'll probably use them in faction wars) but I'd still spare them
dont feed them but rather raise food(chickens) from mystery shards
-> pull mystery shards
-> start rasing those common and uncommon, level them and rank them up with other commons/uncommons
-> feed your Elhain 4star commons/uncommons
-> you now have a 5star Elhain
Jizoh is actually decent in Faction Wars at least in the beginning and you'll want Shaman for her revive in Faction Wars too but you dont want to focus on that atm, thats for later, lvl 40 will do there for the time
Elhain is the better nuker by far, you can get Hexia to 5star later if you want
you'll fuse Broadmaw at some point but this early on you shouldnt go for him he wont improve your team, also the uncommons are easy to get. later on you'll have loads of Mystery shards. so feel free to use them for feeding (not the void rares tho if you already have some)
you'll want to get Warmaiden from campaign she is well worth taking to 5star and you can farm copies of her to book her. drops in Campaign 9
you'll use her in Campaign /dungeons/Arena until you get a better Aoe Defence down champion
edit: Hexia is alright I guess, btw her and Deepheart I'd take to 5star first which ever performs better for you. her Def down on A1 is useful but you want a more reliable version and aoe of it, hence Warmaiden