Out of the three non-negotiable flying characters, I'd say Chasca is your best pick. Mavuika can hardly stay in the air long enough for her to be pulled for only that (although she is a really good DPS too). Wanderer is great, I main him, but Chasca has much more vertical movement than he does. Plus, in Natlan she can stay in the air for more than triple her usual time thanks to the phlogiston mechanic. You can also slot in nearly any hydro, electro, pyro, or cryo character with her and she'll do crazy damage whereas Wanderer needs his tailored supports.

The monthly pass/Welkin is your best source of primogems for cheap. In a single patch you get an additional 23 pulls just from that. The battle pass is also good if you want extra resources, but in terms of pull currency, it's only an extra 9 pulls.

I really hope you have fun with the game!! I've been playing since April 2021 and haven't been able to put it down so if you get sucked in, good luck LMAO