I don't think it'd be a big deal so long as it was an enchant still weaker than a single perk investment at low skill value. That way the perks don't get undervalued. And I'd suggest fairness for the rest of it, custom armor orders and upgrades. Choose your potion.
Totally fine by me. Plus I don't think the OP is asking for something that's equal or better than what a fully trained and spec'd enchanter can do. The OP just wants to the option to have someone other than his character do it so he doesn't have to break his roleplay format for his particular character.
With the custom armor orders, the smith in Whiterun could be the only smith available to make the higher tier stuff, but in the same way the suggested NPC can't make as good/better enchants, I would restrict the npc smith from making anything better than dwarven (ie no dragon or daedric). Not sure how I feel about Ebony, could go either way. More basic armors could be made by more run of the mill smiths across Skyrim.
I don't really care how you work custom potions. There's enough +skill, +health, poison, etc potions in dungeons or on merchants, that I don't know if it's really needed, but I'm sure there's folks that would like it.
You want to be able to bypass an entire skill tree with extra gold.
I don't think he's saying that. I don't see a request anywhere in his OP that he wants double enchants or anything like that. He just doesn't want his character to do the enchanting if it doesn't fit his rp role.