I do not know anything at all about foot fetishes, but as something tangentially related, do not recommend that you return to Catholicism RIGHT NOW.

This is because your short OP contains an extraordinary dose of judgment. You are trying to draw some lines. Trying to define what is and is not sexual (as if anybody truly cared). Trying to control what turns you on and to what degree (largely impossible). Trying to rank the possible degrees of foot fetishism - do you have it at all? if you do, is it borderline or full-blown? is it bad or worse than bad? etc. etc.

So all of that bespeaks a huge amount of YOUR GUILT about sexual behaviors, so, I think, you should not - right now - hypothesize about whether potential partners from among Catholic women would feel guilt over how they use their toenail polish around you. You have lots of guilt in your own mind to work through BEFORE approaching other people. And to the extent that Catholicism has a reputation for instilling MORE guilt related so sexual behaviors (which is not true of all the denominations and variety, but in generally is accepted as fact), you clearly do NOT need to return to Catholicism RIGHT NOW, because it would be courting disaster. I think you need to stay within agnosticism and atheism and whatever it is that you presently are alternating between, and in that framework try to grasp the notion of "harm to others and self" as well as the notion of "consent and mutuality". Somehow those notions are totally absent from the OP. You wrote quite a lot, but there is no mention of your recognizing that the standard applied to fetishes has nothing to do with specific body parts and everything to do with whether somebody gets harmed in the process.