wiring components

That one is up to you.  Some people mount the crossovers in the doors, others mount them back with the amplifier. 

If you want to mount them in the door it is important that you protect them from moisture that can develop in the door.  You'll also need to find some way to secure them to the door so they aren't flopping around.  Some people put a ziplock bag around the crossover then mount it to the door. 

Which amplifier did you end up buying?  100w is a lot for those components.  Really be sure you put a high pass crossover on them to protect them from abuse. 

You should know that it is important that the component installation is well done.  A good component install can make OK speakers sound great and a bad install can make good speakers sound horrible.  

To answer your question about wiring, sometimes you can fit the new speaker wire in with the wiring bundle aleady coming through the door.  Other times you need to drill a hole.  I slit a small hole in my rubber wiring boot on the door side, thread the speaker wire through, then sealed it back up with silicon caulk.

To mount the speaker you'll want to be sure there is a great seal between the speakers and the door.  A cheap solution is to use a cheap foam baffle from crutchfield.  http://www.crutchfield.com/S-WEtFJigoQoa/cgi-bin/ProdView.asp?g=762&I=237XT65&search=foam

I also remember you talking about putting this in a 6x8 hole.  Be sure the MDF bracket you make is also well sealed to the door.  Any hole you have between the front and back of the speaker, even a little one, can cause cancellation and lower your midbass you get from the speakers.

Let us know what your plan is. Hope this helps.