Is it okay if I dont have my watermark on my pfp if I put it in the stable bio? The avatar size is so small I feel like fitting it would be difficult. I haven't played HEE in years and I'm just getting back on the horse now (pun intended) so I'm a little rusty on the copyright rules.

Yes you have to put credits on everything otherwise it'll be taken down because mods can't know who it was made by or what photos were used.