the strenght of caapi cant really be generalized by the advertised color unfortunately, it depends on vendor and possibly other factors (where/when was it harvested, age of vine, if it was correctly identified, etc).
So the best you can do is first try a small amount (10-20g) to find out strenght of your particular batch (or try to find someone that bought frm that same batch, maybe check suppliers subforum)
I suggest first brewing without the admixture till you find the strenght, then you can mix the admixture.
Ive had supposed red caapi that was potent at 40g, so in that case you would have two very strong doses or 3 medium-small ones.
As for storing, as with everything, cold, dark, airtight.