If possible you should have the non-epic quests earlier in the game and the epic quests later in the game. I think it's good to have both though.
there really is no "earlier" vs "later" in the game, unless you measure it by number of days alive, or total skill exp, etc. there's no over-arching storyline where mundane tasks might appear early on (like tote shields for the companions in skyrim) with more epic undertakings later on in the story.
both quest and random encounters are scaled to party strength, the difference being that quests range from a single 1st level opponent on up, while random encounters have a minimum of one and a max of num_appearing for that animal type. but you might still encounter a single 10th level animal while at 1st level (so to speak). so random encounters may be imbalanced with a weak party vs a single strong animal (sabertooth! time to run!), or they may be imbalanced between a strong party and a small/weak herd (rhim gazelle! time to hunt!). quest encounters are carefully scaled to always provide as close as possible to, and no better than, 50-50 odds in favor of the player's party.
almost all quests are "random encounters" that can occur at the shelters of friendly bands: "the cavemen here tell you of a great treasure... go for the treasure? yes, no.", that kind of thing.
i was thinking that mundane tasks/jobs might make sense from both gameplay and immersion standpoints. its more stuff you can do that might have occurred in the real world. and given the random encounter driven design of the game, from bushwhackers to sabertooths to catching a cold to montezuma's revenge from drinking dirty water, even a mundane fedex or escort mission might turn into quite the little adventure.
it could potentially almost double the number of quest types possible, such as escort quests with and without a special quest encounter. tasks/jobs for those who want them, and epic challenges for those who seek that. between the quest and random wilderness encounter scaling for party strength, both jobs and quests would be appropriately challenging. about the only challenge in implementing it would be determining the proper reduced reward for jobs vs quests. maybe start at 1/2 quest treasure levels and adjust as necessary.