As usual, a bang up job. Glad to hear you finally got some good advice from someone re: components. I've landed on Alpine head units myself after years of being a slave to Sony.
Some words of advice. As you apply more layers of fiberglass, the two layers you currently have will start to fold in on themselves and distort. The way to keep this to a minimum is to roll out as much of the resin as you can so the resin/matt ratio is as low as possible.
You've probably figured out the fleece stretching idea if your looking at MDF rings for the speakers.
See what the air volume is for your mids. I used Quart Q's for mine, and the volume requirement is much more than a kick panel pod can fit. If you find the sound is small and restricted in the midbass area, an awesome way to fix it is to port the enclosure.
I had cut a hole in the metal near the bottom of the kick panel to access the heater tubing connection for the hose that heads up to the top dash vents, as I couldn't reach the area any other way. I was able to use hose clamps there to solidly mount the flex tubing.
The hole in the metal allowed an exit point for the vent in the back of the enclosure. I used some sticky sided weather proofing around the vent and sealed it to the hole in the metal, allowing the backpressure to vent to the luggage compartment and not into the interior. The sounds was instantly improved and the depth of the midbass much lower.
I also have my sub up front to keep the sound all coming from the front and to try to neutralize the rear weight bias of the car a bit. I really have liked the results.
http://www.geocities.com/volkdent/BugInterior.html
Jason