I will first direct you to two resources where you really should do a lot of reading. The questions you asked are all answered in one of these to locations.
MP3Car FAQ: http://www.mp3car.com/vbulletin/advfaq.php
FAQ Emporium: http://www.mp3car.com/vbulletin/the-faq-emporium/
A Carnetix unit is your most likely bet. It all depends on the power requirements of your specific model of laptop. Check the output voltage on the AC power brick, and it should tell you.Power supply / On-off controller: Is this one unit or several units? Can you suggest what I should use (cheap as possible)? I want DC-DC...no DC-AC-DC conversion.
You can get cheaper touchscreens, but you're going to take a risk as far as quality and/or reliability.Touchscreen: Are there cheaper/good units then the lilliput screens? I'm looking for a 7 inch. Can this be connected directly to the motherboard or graphics card so that the pc recognizes it as the primary display? How many cords feed off the touchscreen?
A touchscreen w/ VGA input will connect to the PC's VGA port, just like any other monitor, which would be the PC's primary display.
Generally three: VGA, USB (for touchscreen) and power/ground.
Nobody can point you to a concise DIY write-up simply because there is none.Can somebody help me out...perhaps direct me to an article that gives very concise DIY instructions. THANKS!
Every install is 100% unique with its own challenges and hurdles.
That being said, you can glean a lot from other users' installations. I suggest checking out the Worklog area and the SOYP area to see what others have done, especially with laptop installs. Most users' are happy to answer questions and give advice.
One suggestion that I give to EVERY newbie to this hobby:
PLAN YOUR ENTIRE INSTALLATION BEFORE PURCHASING ANYTHING.
You're going to save yourself money and headaches, I promise.
Welcome to the madness and good luck to you.