There is some great advice in the forum for new players like yourself, here’s just one… Advice for New Players, or "All the things I wish someone had told me when I first started."
I agree with this statement as the higher level heros like Vela and Marjana are very expensive to level up. Not sure if you’re involved in alliance wars, but you’re going to need 30 heros as a bare minimum.
Fast mana heros like Bane, Valen, Namahage & Berden are great, especially if you don’t have a healer yet.
Link to information on the last Avalon event below. Building at least 3 rainbow teams of 3* heros is a great idea. A healer like Belith would help to conserve battle items.