2) filter, always blog on topic, if you create a "big boobs" it's about the niche, not the sponsor isn't it ? doesn't matter if it's not specific for big boobies, your visitors might like whatever else they have and you could get a sale from it anyway
if you put up a picture of a milf with big boobs that goes to a milf site they might buy a subscription there, and it's actually ok to do this every once in a while to give your visitors some fresh stuff and not have them see the same specific big boob sponsors over and over
1) about keywords... that's just subjective, you'll have to try it out yourself, but don't use the same keyword over and over, like "checkout this big boobed hottie as she takes a cock between her big boobs and then rubs her big boobs with it", that would be too much imho, but like i said it's subjective
