It seems like a Mage is likely to cast force 4 spells a lot to avoid drain (assuming drain dice pool of 10-12). Is this true?
Since spells have different drain values, you're best off deciding what the highest drain value you're comfortable with is. Three drain is usually low enough to expect to resist it all on average, which means F6 Lightning Bolt, F6 Punch, etc. For buff spells, you'll usually have to accept at least 4 unless you use reagents because you need the higher limit and many of them have DV = F for drain.
The easiest way to increase your drain resistance pool is via Increase Attribute spells. If you have Focused Concentration high enough that works, but I've built some characters who purposefully only have a 4 base in WIL so they can begin with a F4 Sustaining Focus (Health) and use that to sustain a F4 Increase Willpower. With an Elf, you can easily have 8 CHA and 4 WIL base, meaning that'd be 16 dice to resist drain.
Alternatively, be another metatype and add Focus Concentration 6 and rather than 8, have 6 LOG or CHA and buy the appropriate Inc. Attribute spell for that. That can have you with 18 dice and no penalties for sustaining the two spells. And you probably didn't even take any drain damage from casting them, so you're good.
Then, since you either have 10 LOG or 10 CHA, you'd be pretty great at, say... First Aid or Negotiation, whatever you build for.
Or Intuition! Forgot there's Intuition traditions. Oh man the Perception and Assensing dice...