Don’t have any 5* purples. Have Merlin at 4.70 and C-Tib and Cyprian at 3.70 (no mat for the final step yet). At 3*, I have Treevil (LB & emblem), C-Bjorn (LB & emblem), C-Balthazar, C-Tyrum, and Maeve ascended.
Sabina and her costume. Both will prove useful for a long time to come. There are some other good heroes on that list, but they’re more accompanying pieces. Sabina and her costume are roster staples.
My snap decision was Ahhotep, as mana chunk for all is awesome, he hits hard (especially after treevil!) and passives are nice.
On reflection, perhaps c.Sabina would be a more balanced choice.
Both will certainly last a long time into your gaming and are by far the best two 4* choices.
Aqeela and second tree if you want to bling out your 3s
Since you don´t have mats to ascend them anyway I would stick to 3 stars for now. And what you lack there right now is a healer, so go for Para or Aderyn, whichever you like better. After that Aqueela is also absolutely worth having. Especially for bloody battle, but also all other tourney types. A second treevil can make your rush tourney defense even more annoying, so that´s another option after that.
As to the 4 stars: CSabina is amazing and an absolute favorite for healers, Ahhotep is a good hitter. So one of those two I think.
I would also recommend having a counterattacker in your roster, it can be Cyprian, but it can just as well be any other colour version.
Defdown heroes are always useful (eventually you´ll try to get them in all colours, just like healers), so you won´t go wrong with Tibs either, but priority depends on if you have other def downers already in other colours…