I can’t speak about pfsense or router-based configs, I have zero experience there. The Proton website does have openVPN and wire guard manual setup instructions though. You could try it with a free account first to make sure everything works before committing to paying for it. If you’re interested, I can show you the changes I made to the openVPN config file to allow split tunneling. Again though, I don’t know how that translates to pfsense.

The Linux client isn’t perfect, but you can download the openVPN config file and set up individual server connections yourself. It’s all laid out on their website, fairly simple. If you know what you’re doing, you can also edit the config files to allow IP-based split tunneling.

Proton has their own cloud storage called Proton Drive. If you buy the top VPN tier I think it includes all of the premium Proton services, Drive included. I think it’s like 500 gigs for a single user account and 2 terabytes if you get the family account.