I had a mailorder where I sold mainly vinyls but with the times and the orders I started to sell also shirts. I had the opportunity to sell hoodies too but I bought only 1 for me, the quality is still perfect but it was too expensive. 12" and 7" were for fanatics like me but I can say that I didn't expect to sell a good quantity of shirts so my suggestion is to try to start with shirts checking also the postage costs... Good luck!
1990-2022 Stalinorgel - https://www.youtube.com/watch?v=pV-Xppl6h8Et