Also if I start with 4-6 gbr and thin out to 1-2 pairs and add the festivums last I should be okay? Do I need to sex the festivums or will they be aggressive?
For tetras serpaes or lemons would be good. I’ve had sevs eat small fish so bigger tetras is better.
Your plan for when to add is good, I’m pretty sure festivums are pretty tame, same sex is probably best because if they pair off they may harass the third wheel.