What you want sounds more like an evocation maneuver. If your group thinks it's within the bounds of the element you're using, you can totally give someone a PUMPED UP Aspect with a quick evocation spell.
I'd be more concerned about the potential abuse of psychomancy if used through evocation.
Aside from that, a ritual could just as easily be a concert or individual song (depending on the size you're going for) as it could a traditional one with circle and candles. A couple of declarations/manoeuvres like
In Tune With My Magic or
The Crowd Follows My Beats would be used in the same way the orgies in Storm Front were; to generate the right kind of energy (aspects) for the ritual.
As for hexing; a circle of cords around the practitioner would theoretically allow you to set up a guitar without hexing the rest of the stage equipment. You'd probably go through a fairly big stock of guitars though as they'd be getting the full force of the guy's magic in an enclosed area.
So he'd set up the circle (Declaration), play a few songs (Performance Manoeuvres/Declarations), maybe invoke some aspects, then break the circle and start to roll for control. Hey presto! Instant ritual!
Skills:
(+5) Conviction, Performance
(+4) Presence, Scholarship
(+3) Deceit, Discipline
(+2) Athletics, Endurance, Lore
(+1) Alertness, Contacts, Intimidation
(total 33)
These are fine, though mind mages are often all about control, and once they have a few Lawbreaker stunts under their belt they're much more likely to use Intimidation in social situations. Might want to keep that in mind for later on in the campaign.
Powers
[-2] Channeling (Air, Power +1)
[-2] Ritual (Psychomancy, Complexity +1) - (should have 8 complexity shifts?- see below)
--Lore(2)+Aspect(2)+Ritual ([Stage{2}+Components{2}=4)=8?
Did I get that right? And this could go up if he can apply more than one aspect at the same time?
Not quite. If you want to note down potential spells, they should probably go in a separate section. I usually note my Power lists down like this:
[-2] Channeling (Air, +2 Focus Item Slots)
[-2] Ritual (Psychomancy, +2 Focus Item Slots)
For the ritual you're wanting to make I'd go for something more along the lines of a multi-zone ritual to create Stage Aspects over the crowd. These would then be used as Compels against the crowd/players (you can Compel the players to roll Discipline to avoid having the mind mage enthral them or just have it as pay a Fate Point or Be Enthralled, though I wouldn't do the latter unless this was a grimdark campaign). Either way, this equation works as a decent rough guide for working out how much complexity you'd need:
Complexity = Zones * Stage Aspects per zone (3 as default).
So if you have a stadium full of fans, making up four zones (Stands, East Seats, West Seats, Refreshments) and you want to place one aspect on each zone you'd have a final complexity of 3*4=12. With your Lore +2 and Focus Items +0 (you'd be using Complexity Focus Items here) you'd have to create/invoke 10 aspects to reach the final complexity.
Alternately you could set up the confrontation in such a way that the players are forced to be subtle in preventing the ritual from happening; revealing the existence of magic to a crowded theatre/stadium would not be something the White Council would take kindly to, for instance. Of course, if your players are anything like mine have been, they're just as likely to pull the fire alarm as anything else.
Stunts
[-1] Spellsinger -- Use Performance instead of Discipline for control
[-1] Occultist (Lore) - Music+1, Ancient Music+2
[-1] Art Historian (Performance), Art=1, Music History+2, Rock Music+3
[-1] Poet (Performance) Composition+2
[-1] Scholar (Scholarship), Music+1, Ancient Music+2
(total 9)
These are fine, though if you plan to have your NPC fighting the players you may want to adjust one or two to be more combat focused.
Focus Items
Guitar [Vintage '57 Fender Stratocaster], [Air, Offensive Power (Conviction)+2]
Guitar Pick [Air, Offensive Control (Performance)+2]
These work.
Rote Spells (Bound to Focus [Guitar])
Riff #1 (Creates Wall of Air) Movement Border [Defensive Power (eight) {to target roll Performance} for 1 Mental stress]
Your guitar is an offensive focus while this is a primarily defensive spell. You also don't need to roll control for rote blocks. They just happen. Regular blocks require a roll, but that's only for control, not to aim (I made this mistake in the first campaign I ran).
Riff #2 (Feedback), Attack (audio), Offensive Power (Weight) [to target roll Performance} for 1 Mental stress]
Base Spell Power = Conviction(5)+Channel(1)=6 +Focus[Guitar(2)]=8
Base Spell Control = Performance(5)=Focus[Pick(2)]=7
You don't have any specialisations as a Focused Practitioner so your base power is 7, not 8. Control is fine.
If you had taken this as state (8 power, 7 control) you'd have to take 2 points of Mental stress every casting as you always take 1 to cast a spell + 1 from backlash (unless you went with fallout, which would be interesting to see).
I need to know if the math is good. If so, is there a problem (rules or concept) with him using a "Spray Attack" on the amplified music from his guitar to hit a group of people at a concert with his Psychomancy? (He's slowly creating a mob of truly fanatic fans this way.)
You'd probably use group attacks or stage aspects for this rather than spray attacks; they're more efficient at targeting large numbers of people at only -2 to power.