HCG 500iu/wk starting around week 3 or 4, whatever you want, run until the start of PCT.
Also, just because you switch from test e to test p for weeks 10-12 doesn't mean that the enanthate attached to your drostonolone isn't going to keep you shut down for two weeks after its last injection.... are you sure this is drostonolone enanthate and not propionate? If it is enanthate, you might as well run testosterone enanthate up until week 12 as well.
Either way, you have no need for masteron. 20% BF is really high and masteron won't give you the "hard" look you read that it will give you unless you're at least below 10% (if not more like 7 or 8). So I'd say lose some weight naturally or do a test e only cycle and cut.