Finalizing system plan- need advice!

Greetings- My 2005 e46 M3 should be at the PDC any day now (depending on how much the hurricane's interfered with transit), and I'm finalizing my system plan. Desperately need advice in a few areas;

So.

Vehicle: 2005 BMW e46 M3 coupe
Head unit: BMW OEM, ***with differential balanced outputs, ~12-13V (NOT line/RCA outputs)***
Main speakers: Focal Utopia 165W w/ seperate crossover. Nominal power 100W, max power 200W at 4 ohms. Two pair (with rear attenuated as required for fill)
Subwoofer: Focal Utopia 27WX (for sealed enclosure in trunk over battery box). Nominal power 250W, max power 500W at 4 ohms
Main speaker amp: Zapco 1000.4. 4x150@4ohms.
Sub speaker amp: Zapco 750.2. 1x750@4ohms. Zapco DBC to work in conjunction with the amp.
Main power will be by a Optima Yellow Top, running through an AlumaPro Cap5 to the amps.

Is this a solid system? Here are the concerns-

1. I realize I'm way overpowering the rear speakers if I'm attenuating them down for fill, but I don't see any other option. The only way to drop the power would be to go to a separate 2x100 amp for the front, and a separate 2x50 amp for the rear- I *think* staying with a 4 channel will make all the wiring easier as well as balancing the system.

2. Am I going to blow up my sub with this configuration? I've heard that the Focal's are very underrated power wise, and also like a *lot* of power. As I see it, the only other option is the Zapco 500.1 w/ 1x360@4 ohms. I'd assume it's better to overpower than underpower since it will a) give more headroom, and b) the power output can be regulated. BMW trunks are notoriously tight sealing, so in my mind, more power is better to punch through the trunk. Unfortunately, the sub I chose is limited to single coil, 4 ohms. Is 750W the best choice or should I drop down to 360W? The only other option I see is to move up to the Focal Utopia 33WX (13") sub- it takes more along the lines of 500/800W, but it is listed only for Bass Reflex enclosure, not sealed. Ported is not viable since the sub will be over the battery box. Could I use this sub anyway in a sealed configuration?

3. Will I get reasonable sound out of the 11" sub in the trunk, or do I really need to go to a 12-13" to compensate for the tight seals? I don't want to cut panels or install the sub anywhere else other than the battery cover; the whole point is to have great sound with minimal loss of trunk usability.

Everything being said, if I can't get the 165W's to fit without cutting metal, we're back to Plan B, which is Diamond Audio.

Again, much thanks. Rod.