Blindsight won't be added to any class, since it's basically unnerfed true-sight (on a server with very much nerfed true-sight). Perhaps a spot/listen bonus while in sewers instead? They already have a bonus to spot/listen however.
As for vs enemies, the way it works in NWN likely doesn't allow for any sort of 'advantage' vs them.
I don't know if crafting levels can be added as class features, infact I would err on the side of they cannot. I don't think this could be carried over to POTM aside from perhaps a lore boost but I don't know about how well that fits with the PnP bonuses. Lore IS a requirement so it could make sense.
I think the most you could ask for is vile adversaries (favored enemy) vs oozes. I have no idea what fungi or carrion creatures would fall under and crocodiles would just fall under animals, which may be too wide of a net for a class to acquire as their first level feats. Perhaps later on in the progression, as well as the scaling up to +3. +1 at 1, +2 at 5, and +3 at 10. This also gives more reason to go full 10 levels.
As a note on the favored enemy (oozes), in base NWN it cannot be selected so I am unsure if it can be selected on POTM or if the feat choice exists to add to a class.
Grimetrekker is a cool but I don't imagine very often picked class. So it'd be pretty cool to make it more desirable.