Just hit level 40 so I can start doing Zero system but wanted some advice if possible.

This is my current roster, so far I've been using those 9 units but for what I've read resources are quite scarce later on so I was wondering what 2 teams should I focus on (I do get that in time I should be able to get them all to max but would like to have something set that will carry the rest of the units later down the line)?

Also, I know I am trigger happy regarding pulling (please don't judge) and ended up not saving the free currency I get but I am now wondering if the selector at 300 will retroactively include new units as they are added to the standard pull.