Well I’d be okay with p2p but I know most people wouldn’t be.
So I say go the Dota 2 way, make all the content available. Make the cosmetics tradeable and buyable. Have like Dota 2 a store, maybe even chests and such. Just make it all about cosmetics. I know people that farmed for weeks to get a cosmetic in RO1 hell I did it. I bet some peeps would pay 200$ for some Tree of Savior cosmetic.