is there anything you would recommend?
You'd need to donate via whatever means they accept donations, it's not something you get to choose yourself. Unless you meant that you are going to keep contacting FOSS projects to ask them to set up new donation methods?
Personally I donate via crypto or other means that they allow donations via credit card (Liberapay / Ko-Fi work well IMO) . No Paypal/Venmo since I can't use those services - some FOSS projects I don't donate at all if they only accept Paypal.
Yes you can still seed as well as download. But you are limited and can only upload and download torrent data in swarms that contain peers that are themselves fully connectable (port forwarded).
So say you join a torrent swarm that only contains peers just like you (firewalled, no ports forwarded) then no one will transfer any torrent data with each other. Everyone is stuck waiting for a fully connectable (port forwarded) peer to join that swarm.