I'd like to stay away from the Boogeyman for several reasons:
1. Mechanically, it just doesn't work as a good character, and I'm not really enthused about hand-waving Soul Eater into a non-evil class.
2. A character who feasts on the souls of others (deliberately or accidentally) really doesn't fit with the tone of the setting.
3. The Boogeyman's at a higher OL than I'm really aiming for with this game. One of the major themes of the Myth series is that teamwork and cleverness--not raw power--get the job done. Of the two major characters, one is a wizard with no magic, and the other starts as an apprentice wizard with minimal spells. Although he gets considerably more skilled by the end of the series, he's never the kind of world-levelling powerhouse his reputation makes him out to be.
Most of this will be covered in the new post. In general, though, take the base Druid as the benchmark. If it's significantly more powerful than that, it's probably not a great fit for this campaign. I won't say no out of hand, but it'll factor into the decision.
Gnomes (and the other default D&D races) will also be covered in the new post. In brief: any default race from the PHB is fair game; it's just that some may not have the same name. ("Human," for instance, would include Klahds and residents of quite a number of other dimensions.)