Advice on which characters to focus on? Which G13?

If you aren't sure, there's no reason you have to relic anybody at all.

Warren Buffett notoriously said that he says no to all business deals unless his assessment of them is an unequivocal "hell yes." I try to apply the same logic when allocating resources in SWGOH: if you aren't sure it's a good use of your gear/zetas/whatever, just hold off.