@hazard has given you excellent advice! I’m in to this game the same length. I was frustrated waiting for ascension items with 4* I couldn’t level that I focused on. @Kerridoc gave fantastic advice on building a strong 3* rainbow team, then strong 4* rainbow team before even attempting 5*
I would build the staple 3* heros first. IMO they are Brienne, Belith , Bane, Balthazar, Nashgar, hawk moon, valen. I have 11 on my roster and still use them, mostly only for challenge events now, but that’s because I have almost 3 fully levelled 4* teams. On my alt account I haven’t even touched my 4* or my only 5* Delilah, I’m building my 3* roster. It’s better to fight with fully levelled 3* then partially levelled 4’s and you need to collect more ascension items.
You have some fantastic 4* heros, I would level Bold Tusk first and you have the items for him. Then Grimm, Wu, Rigard, Peters and Sonya. You will be very competitive with a solid 4* rainbow team. I am often top 3 in my alliance in Titans with my 4*'s over people with partial 5*