Ronin: Spell Hawk from Quintessential Wizard seems to be a bit fudged by my reckoning, though. Counterspell Riposte was described earlier in the thread; a metamagic feat that adds +2 to spell level, but after successfully counterspelling a spell you can use the enhanced spell as a free action in response. I don't know much about sorcerers, but as I understand it they take a full round action to cast anything with metamagic since they don't prepare spells ahead. So this feat seems null and void for them. And yes, the feat does stipulate it has to be an enemy spell. So no having some 1st level sorcerer you've hired go casting cantrips so you can pop off a quickened spell for half the cost and outside of your turn.
the spellcraft skill: the important component to any counterspelling.
Agreed. I have never played a sor/wiz that I didn't max Spellcraft, but the importance for a counterspelling specialist bears more emphasis. If not planning on the Loremaster PrC, it would possibly be worth adding Skill Focus (Spellcraft) if the feat were fixed to +3. I'd like to think they will make that fix with 3.5e. Potential Loremasters have to use the Skill Focus for a Knowledge.
the feat spell focus and its more powerful variants would also be helpful. as would a high int. maybe skill focus (spellcraft). and more importantly improved init. since you must have your counterspell readied to use.
What schools would you recommend spell focusing and why? The only one I'd ever really consider would be transmutation because of the nice mix of debuffs and attacks. If not pursuing Loremaster, I would trade the Skill Focus for Spell Focus (transmutation). But I'd pursue Loremaster for its benefits and roleplaying value.

Having mini-bardic knowledge and Use Magic Device is nice. So far as Improved Init, it's a prereq. for Reactive Counterspell, which lets you counterspell without a readied action. When I reread the feat I realized you don't even have to delay your action, because counterspelling after your turn in an initiative round takes away your action from the next round. Now that's some flexibility.
1) the amount of magic in the campaign. just how many spellcasters are you likely to meet or battle? if you look at the rules for generating a typical town or city. the majority of the population of potential rivals are noncasters.
People? Yes. Monsters? No. And against mundane opponents, a wizard is far from helpless no matter what feats they take. (If this thread seems to ignore sorcerers, it's due to my lack of interest and experience with them) My own preference would be to prepare a "random encounter" repertoire that mixes any combination of dispels, buffs, debuffs, attacks, and general utility spells. But at higher levels the right divinations allow for much more deliberate preparations in planned encounters.
2) what are the benefits to using all of your available spell slots in the hopes you will get to use them as a counterspell? or if you decide to cast them as normal, what are the risks someone will counter you?
No need to use every spell slot every day or encounter for antimagic duty, but the feat progression would mean the character truly excels in that capacity as opposed to sheer damage, item creation, or anything else. What's the risk of an enemy using their own magic to counterspell you? If that's all an enemy does then it means the rest of your party has a free ride in ripping them a new one.
3) how many feats do you get? and if you use them to bump up your counterspell effectiveness can you now use them for other purposes?
A human Wiz 10/Loremaster 10 ends up with 11 feats. 7 feats for character level, 2 metamagic feats for Wizard levels, and 1 racial bonus feat. That leaves room for the feats I've asked about in this thread and some padding as well to spend on extra metamagic, item creation, or anything else. The most impressive thing about a Wiz 10/Loremaster 10 though has to be the skills and special abilities.
diaglo: If you were going to DM a game, what would your opinions be on converting Focused Dispel into a feat and adding a Greater Focused Dispel? Your opinion on Counterspell Riposte? Mastery of Counterspelling converted as a feat with the appropriate prerequisites?