I recently leveled/merited BST, and this is what I gathered.
5/5 Call Beast and 5/5 Reward is your best bet with Group 1.
Group 2 is...mostly your decision.
Either 2/5 or 5/5 Beast Affinity.
Basically, NurseryNazuna's pet level caps at 86 by default.
With 2/5 Beast Affinity, it caps at exactly 90.
However, when the 95 level cap comes, you would need 5/5 to make Nazuna's level cap 96, so that you'll have it capped at 95.
So, you can either get 2/5 now and redo your points later, or go 5/5 and be good-to-go.
I recommend either 5/5 Beast Healer or 4/5 Beast Healer + 1/5 Feral Howl.
Feral Howl doesn't work on pretty much everything that matters these days, so most have deemed it useless for now. But it has a few uses in old zones, I suppose.
Killer Instinct is pretty situational, I don't find it worth it, but could put a point in it if you can find a use for it.
...so in short what you were thinking is pretty much fine.