honestly, I'd steer clear of one penis policies. usually the guy is insecure and or doesn't really want to be poly (if the wife is allowed to be with women). I met a guy like that and now none of us involved are on speaking terms.
all that being said...I struggle with the "primary" stuff with my boyfriend. You have to figure out what you want and ask for it, also taking his other partner into account
keep on keeping on