Characters have a max mana and a recovery rate.
Continuous self-buffs and party buffs reduce your max mana while active. They should take a large enough amount of time to turn on/off that you can’t do it easily in combat.
Your recovery rate applies during rounds in which you did not actively cast a spell.
Abilities which have significant recurring non-combat value or are ‘at-will’ should be considered continuous (e.g. telekinesis/mage-hand, 4e style at-wills, 3e-style reserve spells) and can’t be switched on/off at all, except in special circumstances or during significant downtime.
Most spells with any kind of duration will default to 1 round.
You can spend more than the default mana cost to improve a spell. What attributes can be improved will vary from spell to spell.
Some spells will have variable duration at cast time. Others will have the ability to be “sustained” by taking a action (standard? move? minor? something else?) each round and spending more mana to keep them going.
Levels of magery: dabbler, adept, expert, master (needs work)
- Specialist: You advance faster in your chosen school, but are limited to that one
- Generalist: You advance more easily in all schools, but can never reach Master level
- Non-mage: Can never cast, but some other benefit?
Reversible spells, which helps make the overall spell list simpler
Rather than list lots of spells of different levels, have spells with basic effects, then improve them as the mage gets Adept, Expert, Master, whatever. Example: Push/Pull moves an enemy further/closer to you. At Adept, maybe you can do area effects with it now, and at Expert you can do an area not centered on yourself.