GMMichael
Guide of Modos
Morrus, what you've described sounds very similar to my game. So I can say with confidence: your idea is starting off on solid footing! Some thoughts:
If everybody gets "spells," while the mage gets 1 HP and the warrior gets 4, then the mage won't be a very popular class.
The opposed-roll thing works great.
Classes-defined-by-skill works great, as long as your skill list makes sense. For example, you don't want a 10th-level rogue who's an ace at Pick Pockets but can't Distract someone to save her life (since they're related skills). Also, a 20th level mage might wonder why his Wealth is still garbage.
I hope I'm not preaching to the choir
Why not just scale by level - a 10th level character can't exceed +10 skill points?(also thought needs to go into the scaling -- like this a 10th level character will be at +20 in the thing they're best at)
If everybody gets "spells," while the mage gets 1 HP and the warrior gets 4, then the mage won't be a very popular class.
The opposed-roll thing works great.
Classes-defined-by-skill works great, as long as your skill list makes sense. For example, you don't want a 10th-level rogue who's an ace at Pick Pockets but can't Distract someone to save her life (since they're related skills). Also, a 20th level mage might wonder why his Wealth is still garbage.
I hope I'm not preaching to the choir

I faced that problem, and came up with this: establish a baseline set of skills. Each player-created skill needs to either branch off one of the baseline skills, or be comparable in scope (subject to GM approval). Also, since skills will likely interact with the rest of your rule set, you want to establish which skills do that and how that relationship works. E.g. if you have a hit points system, pay attention to which skills affect hit points.I like where you are going with this, but whenever I see systems that try to cover a wide range of skills and class, I find myself wishing there would be a system that from the base rule would let players create their own skills and their own classes. I've played around with this but never came up with a good way to have such a system that remained balanced and was at the same time simple--or at least not overly complicated.