I like the concept! When I envision characters, I think about how they will be from level 4 to level 12. I don't worry about higher, because one spends little time playing there, nor lower as levels 2 and 3 typically fly by. With that in mind, the first thing your idea makes me think about is its MAD nature. For instance, say we take -Hi! I'm struggling to realize a concept:
I basically want to create a Wizard that isn't a library-dweller, but someone who is a bit more grounded and versatile in real-life situations. I mean proficiencies like perception, thieves tools, stealth, persuasion, deception, acrobatics, maybe even survival. Someone who is some kind of magical special agent, but still a full caster (with 9th level spells). Someone who isn't too dependent on his party, but can be a backup face or skillmonkey when needs arise.
I know I could build a Bard, that's what I did before. But I'd like to have a spellbook this time (or at least another base class).
Ideas I came up with are a single-classed Wizard with the "skilled" feat and criminal background (or urban bounty hunter).
Or a two-level dip in rogue for the skills and cunning action.
I also thought about a three-level-dip into Arcane Trickster, but then I realized that the 3rd level really hurts for spell progression.
Whatever I do, none of the options seems especially appealing, the opportunity cost is always kinda high. Nothing has the "wow" synergy a build like bard/hexblade offers.
Any recommendations for a really good/synergystic/spicy build?
I agree that he needs to count on spells, but also...Remember too, that a Wizard can already 'do it all'
wanna be stealthy? Invisibility
Want to overhear a conversation? clairvoyance
Want to be persuasive? Enhance ability
Want to Insight someone? Detect Thoughts
Want to open a lock? Knock
Want to climb up to that room on the second floor? Levitate, Misty Step, Rope trick, Fly, Dim door, Arcane Gate, Teleport,
As many people suggested, Half elf and prodigy will help you pick up skills, tools and boost charisma and Portent will give you a couple good successes/day.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.