I just started a mule and wanted to raise its fame for selling/buying from NPCs. I couldn't find anything in the forums about the rules of questing on a mule. Is it allowed? If so, is it allowed to do the 'higher priced' item quests like scrolls?

As long as you can complete it in a city, you're fine. Mules are only allowed outside of cities for two things, travelling from city to city, or leveling to 10. Quests that require you to do things in open world or dungeons, are not mule-friendly.

_________________

and your mule can do the minimum steps necessary to unlock the mog locker