I can get down with Apo. You have several champions I think you'll want to invest in, going forward. He should be a pretty great general content champ for you, for a long time.
Next up has to be Venomage. Will be great in CB, and can certainly work in Dragon/Ice Golem. Not to mention there's your two turn defense down champ on a three turn cooldown when booked.
After - in no certain order - that I think we can start looking at Reliquary Tender (cleanser/revive), Ronda (nuker capable of disrupting passives), HK (speed lead in Arena with upside outside of that) and Umbral (great provoke option, especially in Arena)
Shieldguard, Warmaiden, Relickeeper, Elhain, Shaman, Hyria, Warpriest, Adriel, Jizoh, Broodlord, Yaga, Ripper and Marquess do not need to be invested in. Steelskull, Kunoichi and Skull Lord can have their places but I see them as less of a priority relative to the other champs I'd like to take up, save for Kunoichi who could end up being an ally protect option for us in Clan Boss.