tldr; More drain protection or more spellcasting dice when multi-casting?

I am creating a mage for a street level game(350BP) and am looking for opinions on character generation if I plan to make a mage that more often then not will be splitting his spell pool to multicast. My GM is allowing me to specialize in multicasting for a +2 bonus to spells cast when I split the dicepool which should help enormously. Advancement in this game would be pretty rapid until the characters reach the normal game (400ishBP), then even out. So my pools #s will go up.

My big question is, should I spend all my quality points on Focused Concentration(2) for a total +2 bonus on resisting drain, or would a 5 point Mentor Spirit and Focused Concentration(1) be more beneficial?

My Pool #s:
--Spell pool is looking like 8 dice (Magic + Spellcasting) before any bonuses. With the bonus from multicasting spec, splitting my dice pool currently becomes 6/6 for 2 spells, or 5/5/4 for 3 spells. (The Mentor Spirit if I take it would add another 2 to each number.)
--Drain pool is looking to be about 9 dice + 2 for fetish + whatever Focused Concentration level I end up with. 4 is about the target for drain early on.

Here are some Drain tables (obviously I won't be multicasting lightning bolt in my mage's early career if ever unless things are really bad, it's included as a 'beyond the redline case'):

I don't know which is better but I would take the mentor spirit now just because you can't take it later (I think). It is at least less of a stretch to merely increase your Focused Concentration later. But that is if you actually want a mentor. They do have their downsides.

Get the mentor spirit. Their bonuses tend to be far more impressive than an extra die for drain. It is after all, more important to be able to get the hits to effect objects and make sure you get through high willpower/counterspelling than to be able to use a slightly higher force spell.

I favor more drain resistance personally. You'll constantly be rolling against drain. The consequences of not succeeding on drain are wound penalties that take 3+ hits on first aid to get reduced. The consequences of not succeeding on casting is that you just cast another spell.

The most efficient thing to do in critical moments is use Edge to succeed and not for drain unless its really, really bad drain. That way you can still have your Hero Moment with casting your big spell and still save Edge by having enough drain dice to keep you good for most casting.

A low-BP way to increase your drain pool is to get the martial arts maneuver Focus Will. Although you'll need to devote two complex actions rather than one to pool off the spell, you'll get another +2 to the drain pool. And I'd recommend against investing BP in Focus Concentration unless both Willpower and your other drain attribute are soft-maxed.

One thing to keep in mind though is that this character plans on multicasting. The bonus from a mentor spirit will apply on both spells, so it is even more useful than normal.

The other consequence being ventilated by the guy your spell failed to affect...

I have to agree here. Getting a direct combat spell to hit means that your net hits stack onto the Force for damage, so there is a lot of bang for your buck there.

Let's just use this as an example for the multicaster:

Say after all the creation is done the PC can reliably generate 4 hits and 3 hits on casting and drain. If the 4 hit build is for casting, assume an F5 bolt of some kind, and the opfor generates 3 hits because of Willpower, Counterspelling, etc., then the target takes 6 damage. The mage takes either none to very little damage in return.

If the 3 hit build is for casting, the spell fails and the mage takes none to very little damage, and yes a greater chance of no damage, but the opfor is sitting pretty...