I don't really like rules. Been that way ever since my mom took away my BB gun.
I'll leave the number of recips up to you. I'm betting you're going to do what's best to get your gallery listed at all the places you submit to. I mostly see around 3 recips, so I guess most sites have that as the max. I haven't built a TGP since my mom took away my BB gun, so you know better than me about that.