You can cancel your subscription after payment to get an update. It would be a rare sight, if a dev has the same version on patreon for sale on itch for the same patreon tier and same price. So what you typically see is something like sale price 10 on itch and cheapest tier on patreon with 1 or 2 gives you the current update, while the purchase on itch would give you updates till release.
Paypal does not ban adult payments, but you need aproval of paypal to collect money for adult stuff according to their tos. They do ban cigarettes.