There is no "MUST HAVE"
the plethora of skills and abilities available allow to you tailor your character a great deal, to suit your style of play, and what (in character ) you want your Caitian to be able to do.
If there was a "Must Have" Template, then you may as well take away all the variation on how characters look too, as you may as well be a standard FPS style cookie cut toon.
Space abilities, Ground abilites, bonuses, buffs, attack defence, all rounder, you choose !
just have fun.