Hi guys,
I thought I'd throw in my 2c for what its worth. I am by no means an expert but I did do a hell of a lot reading during my audio installation. I've mentioned it before, but
www.caraudioaustralia.com is a great source of info.
My kick panels were only me second ever fibreglassing project (after my sub box being the first)....so it's not beyond everyone's capabilities! Here are the pics of the kick panel installation:
http://www.manxgallery.org/gallery/album221
In terms of general advice, work out your budget, invest the most amount in good quality front splits (6.5s will give you better mid bass), then the next most important is the headunit , then the sub (one 12in is enough - again just my opinion). Obviously keep some money aside for cables and fittings.
Jaycar has a really good reputation for both splits and amps (a four channel will suffice for what you are after so you can bridge two channels for the sub, and the other two can drive the splits).
In terms of split enclosures, the aim is to have the volume matched to the splits thiele-small parameters (acoustic properties of the driver/s) - so for example the dynaudio front splits I ran in the ragtop had an ideal sealed enclosure volume of around 10.1L. Most people use the door cavity in modern cars to get the required volume (you still need to take care to seal it as well as you can - not easy in an old veedub!). To get close to my required volume I had to wrap the kickpanels around in front of the pedals etc.
Even so I could only get about 7.2L so I had to port the enclosures (again using a recommended port length and diameter calculated via program (available on CAA forums)). It was important to have the enclosures sealed (ie. an air-tight box [complex shape of course]) for best sound quality.
It is all relative to what you want to achieve - I wanted to have a high quality system that was of a standard to compete at car audio events etc. If you are just happy to enjoy some tunes but are not too worried about achieving "perfect sound"....then sealed enclosures aren't really necessary. My brother in law's karmann ghia has just the single skin f/g kick panels available from US suppliers combined with alpine type S splits and an alpine amp - it sounds good and he is happy with it which is the main thing!
Sorry I have rambled.
Alan
Here is the kick panel mid construction: