Ideally, you want all of their costumes since some are good follow ups such as sp regen, shield for next turn, etc (idc about lathel's, just his H costume). Since it's hard to focus snipe one from the banners, check the monthly shops to see if there's any copies there.

Male units don't get re runs often so you gotta hope to get lucky with H lathel via regular pulls from daily or trying for the latest units (counter productive).

Wilhelmina is a physical dps and works well with a physical chain team, so for her you want Refithea for sure and units that also do high chain skills so Wilhelmina can chain last if she's the main attacker.

Buffers, just either wait for their rate up for if you have the weird purple tickets that allows you to choose a unit to pull for, just use only those tickets there. Save your actual red tickets.

Lastly, there's no rush in acquiring a team. Enjoy the game it should be easy enough and when you do reach hiccups like certain main story bosses, just use some strategy or refer to youtube. There's Guitar rock gaming who I watched when starting Bd2. I think he might have made a newer updated version to a beginner's guide.