It also depends on if you using a Tank or a dripper, as a tank needs thinner juice 50/50 or 70/30 and a dripper uses maxx VG no PG added. On 50/50 and 70/30 blends from TPA I use 10% flavor, for maxx VG I use 20%, but that also depends on the flavor as some are stronger than others.
I would do small tests say 10ml for your recipe batches using no nic, that way if it is crap you don't waste the nic. Use straight VG if your a dripper and 50/50 if your using a tank to test flavors out with.
Might try...
7% Strawberry ripe
2% Cheesecake graham crust
1% Sweet cream
Sounds good to me

Happy mixing!
Dan