Problem 1: Neutralize Poison should cure drunkenness. If not, some other spell will.
Problem 2: What is the difference between him drinking 20-proof and 100-proof alcohol? He should always choose the lower alcohol content drink to maximize the number of spells he can cast.
My suggestion is that he can cast spells only while drunk. Create nine levels of drunkenness with varying penalties, and then say that he has to be at least Drunk 7 before he can cast Spell Level 7.
Furthermore, snap him to the Sorcerer spells per day chart. No sense making a second one. Same deal with which spells he can know, but give him bonus spells known (more variety in what he can cast, rather than how many per day) to counter the penalty of needing to be drunk and needing access to alcohol.
He can consume one drink of beer or wine per round, four of weak spirits, or eight of strong spirits. A certain number of drinks give you one Drunk level. Half your CON bonus counts as an extra buffer of Drunk level, so someone with 10 CON (+0) starts at Drunk level 0, while someone with 18 CON (+4) starts at Drunk level -2.
The Whiskey Wizard can make a CON check to reduce his Drunk level by one for up to 5 minutes, sort of like a reverse Barbarian Rage, clearing his head a bit. He gains an extra Clear Head and an extra -1 level of Drunk every fifth level. But like Barbarian Rage, they don't stack with each other, and it's impossible to have both Rage and Clear Head running at once.
By level 20 he would be able to drop his Drunk level as much as -5 for 5 minutes, 5 times a day.
The Clear Head ability is used so he can perform non-magical tasks reliably, then go back to being roaring drunk so he can do magical tasks.
Some feat ideas:
Beer Belly : Your prodigious belly makes it harder to get a grapple hold on you, giving you a +4 Dodge bonus against grapplers. Your body weight is +20% normal. (This would be hilarious on an Elven chick)
Fire Breather : If you hold two drinks of strong spirits in your mouth, and a flame in your hand, you can blow a cone of fire. The damage is 1d6, Reflex DC 10 negates, in a 10' long line. It takes one round to quaff the drink and a second round to breathe. The drink does not contribute to Drunk level.
Iron Gullet : You can make a CON check at DC 15 to ignore the alcoholic effects of each drink. You can voluntarily fail this roll.
Sour Stomach : You're able to puke on demand, which immediately reduces your Drunk level by one. You cannot puke again until you eat a full meal. Your skilled puking also gives you a second save at a -4 penalty against ingested poisons.
Thunderous Belch : If you prepare for one round by swallowing air or drinking quickly, or incidentally if you're already eating or drinking, you can belch very loudly on the following round. Everyone within 30' must make a Concentration DC 10 check or be startled and distracted until the end of his next action (-1 to attack and saves, 3% chance to drop held items). You cannot be startled by your own belch, but your friends can be.
Some spell ideas:
Inebriate (makes target very drunk, but not for purposes of Whiskey Wizardry)
Sobriety (cures a couple Drunk levels)
Identify Liquids
Distill Liquids
Harmony / Brawl (mass area emotion type spells)
Beer Goggles (ugly people look prettier)
Power Word: Forget
Blackout (more powerful sleep effect plus some Forget)
Curse of the Thirsty Throat (target must drink anything at hand, the liquids vanish as he consumes them, at the end he is dehydrated as if he's gone days without water)
Curse of the Teetotaler (target degenerates -1 Drunk level per minute, preventing him from getting drunk)