Riposte definitely requires you to sacrifice your next action: "On a successful defense with Weapons, you may
sacrifice your next action to turn that defense into an immediate and automatically successful attack." Otherwise you would just take that stunt, go full defense on every fight and get an attack opportunity on every attacker, which is kind of overpowered.
Concerning Redirected Force, the idea is, that you place an aspect with as many shifts as you have generated with your defense roll. The attacker has to spend his next action on getting rid of that aspect, or you are going to use it against him. So either you can use that aspect in your next attack, or he is going to use his next action to get rid of the aspect and not to attack you.
Plus: if your action is before your opponent, you can always delay your action, waiting for him to strike, use redirect force and then you have an aspect placed on him AND the next exchange starts with your action, so you can take full advantage of your aspect. I would expect a character with a stunt like that to fight like that, waiting for the opponent to make a mistake and then using that mistake to his advantage.
The character your roommate is trying to create is pretty close to an idea I played around with, although I didn't apply inhuman speed or toughness. Speed is pretty straightforward, he uses his magic to increase his reflexes and so he can act faster, no big deal. A toughness power for a character like that is tougher though. I would limit it to blunt physical stress only, so he would be protected from punches, kicks, baseballbats, that kind of stuff. During his training he simply learned to ignore the pain from those injuries, so they won't have as much impact on him as some other trauma would have (cuts, burns, bullets would hurt him as much as any mortal). Basically this is an inverted catch (instead of everything but one it is only one thing it applies to), this is explained in the description of the catch YS185.
Another thing you might like is a stunt I used for my character. Because he only uses magic to extend his physical fighting capacity, I gave my character a stunt that allows him to usw fists instead of discipline to cast spells. Basically you can supercharge a fists attack with a force effect. There have been discussions about this type of stunt, but I like the idea, because it really fits the character concept, and I don't think it is all that overpowered.
As far as I understand he should be able to counterspell any spell he wants. Depending on how you apply his channeling (with or without the stunt I described above), he might need to be able to touch the spell or at least a physical representation of it.
Hope this helped, if not, just ask again
