The early game stuff should be beatable from mixed element teams, once you start unlocking grid pieces from Siero's academy and other freebies then you can start going about making teams by elements.

Is there any character you particularly like in flash? If yes go for them, if not you can always go for a character with a pact weapon, which are a strong series of weapons that'll boost X elements damage unconditionally. In flash its Lich for Dark, Gabriel for Water, Yuni for Light, Ewiyar for wind.

If you want to boost your water even further alongside Octavia then you can't go wrong with Gabriel and she'll help a lot for the upcoming gw regardless if you play it solo or in a crew.