You have two options (and hey, they're the ones you mentioned in your question!), and it sort of depends on what exactly you're wanting to do.
First and foremost, most likely the advice I give here is only any good until we see the full NPC creation rules in the DMG where hopefully there will be much easier shorthands than what I'm going to suggest.
The by far and away easiest thing to do is to take the Mage NPC, spell swap for find familiar (something you're given full license to do in the rules, and even if you werent...well you're the DM) and just be done. Also add a racial trait to him to make him feel more like a dwarf.
Your other option is to build up a Wizard as if he was a PC. I'd advise against feats and just take the most basic options and equipment.
The first approach is way easier. You have a set CR, you don't have to rummage for the right spells or anything else really. The cons here are that you don't have any scaling rules for the NPC (he's set at CR 6), and he doesn't necessarily feel enough like a dwarf. These may or may not be problems for you.
The second approach has the pros of being fully scalable, and can be built as a dwarf so it will have a dwarf's racial traits etc. On the flip side, we don't have a PC->CR guide yet so you'll have to guess and it's a ton more work than just pulling up an NPC that's already created.
In a lot of ways what you do probably depends on context. If this is a one-off villain for an encounter, use the pre-gen'd NPC. But if this is a long running villain who is worth more of your time, build him as a PC and maybe even level him with the party.
Given that this character is going to be a quest giver, I'd be inclined to create him with PC rules as the customization offered in that set is going to be far better than what's available for monsters right now (in a month or so, I might change this answer, but I just don't know yet). The only caution is that if you make him too much higher level than the PCs then I wouldn't ever (or maybe only on super rare occasions) let him fight with them. (DM PCs aren't a great idea anyways, though, so there's that)