Mk3 Focus Titanium - Audio Advice & Progress

Hello gents,
New to the forums. I used to run old Fords; I've had a fiesta, two escorts and a mk1.5 focus. I came back to the family recently and picked up a Focus mk3 1.0 Ecoboost. Coming from a 2litre turbo I expected a woeful experience, but I'm really quite impressed by it.

I believe I have a Sync 1.0 with the 9 speaker 'premium' Sony system, and whilst very ok, it's not setting my world on fire.

What I'm not sure of is how to tackle the head unit. I've always gone aftermarket, but looking at the extortionate cost of the fitting kits (£110+!) and after lurking on the forums, it seems to me that many opt for LOCs on the stock HU. I've never run LOCs or a Signal Processor, so I'm looking for advice on the best, and most cost-effective way to do this.

My plan:

1. Retain stock HU.
2. Install 4 Chan Amp. I'm current considering The Pioneer GM-D9704. It has high level inputs.
3. Install Woofers and Tweeters. Considering the Focal PS165F kit. Can I skip the crossovers and tweak the midband on the amp?
4. Drive the woofers from two channels on the Amp, and the tweeters off the HU.
5. Build simple, sealed sub box under the false floor of the boot. Design to allow for a second sub box.
6. Install Subwoofer, currently considering the Focal P25F. Drive from two bridged channels on the D9704.
7. When funds allow buy a mono amp (Pioneer GM-D9701). Drive the front woofers & tweeters from the 4 channel, and the sub off the mono
8. Build a second sub box in the boot, mirrored to the first. Fit a second P25F (when my wallet stops squealing) Run them in Parallel (2Ohm) to get more wattage out of the D9701.
9. Move onto tinkering with other things.

All the equipment would be in the boot. So I'd run the RCAs, spliced lines from the front speakers, and new speaker wire down one side, and power down the other. I don't believe I'd need a remote wire for the above setup. I'd run speaker wire for the tweeters at the same time, just so I don't have to pull things apart again.

Alternatively, I could buy a double din head unit that will integrate with my steering wheel controls. Run RCAs to the back like I normally would, and build a similar system to above, without worrying about an amp that has high level inputs or running spliced lines to the boot. I'd likely select the same speakers and sub, but I'm very open to suggestions.

At this point I'm looking for some advice. Has anyone used any of the above equipment? Does my plan seem sound? Am I better of sticking with the OEM HU, or going aftermarket? Am I mad not using a Signal Processor? Should I go for cheaper components / sub?

Any and all input very much appreciated! I'm sure my plans are subject to change, and I'll update the thread with my progress