Is there somewhere that shows a list of enemy creatures and their levels/stats?

So far it's just been trial and error for me. Do I attack those Giant Spiders or not? Are those Medusa too strong for me? Should I attempt to fight those Minotaurs? When I've tried to fight enemies that I suspect will be powerful, they have been, and they have killed my hero. I would love to have a sense of when I am powerful enough to attack certain creatures like Medusa, Giant Spiders, Dragons, and Minotaurs, without my hero having to die to find out. Maybe trial and error is what the developer had in mind to begin with.

Now that I'm playing on Expert level, my hero no longer advises me to the winning potential of each fight, but then again he wasn't always accurate in his assessment of battles anyway.

First not sure if your talking about Eador Genesis or Master of the Broken World. Not that I know if they made any changes to the creatures either way but MotBW should have a downloadable manual from the gog site although not sure if there is a creature list in that. If not you can use the google translated from russian site below.

http://translate.googleusercontent.com/translate_c?act=url&depth=2&hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=ru&tl=en&u=http://eador.com/en/page3.html&usg=ALkJrhiPujWYY-O7RY0KPdWvVD0TG9nt8w

Sorry for the length but just copy paste to your browser.
WARNING this list is for Genesis but don't think they made to many changes so you should still get the idea.

Yep its all about experience, you just have to try and remember. But still after months of playing I often misjudge what my hero can take on. Even knowing all the creatures stats by heart.

Your hero can give you a pretty accurate evaluation of the fight, though (unless that option is turned off for your difficulty?). They often spot the worst traps, such as a solo warrior against a bunch of spider, or a no-magic army facing a ghost. It isn't always accurate, but it limits the slaughter and allows you to make a semi-informed choice.

MotBW comes with a 75 page manual (the manual in the GOG file section has only 21 for some reason). There every single unit of the game is listed with its stats and how you can aquire it (if possible).
Sadly no word on the respective special abilities, but to get a rough idea on unit strength that should suffice.