you say you have been reading here for years but you seem to have missed a hell of a lot of information.
Your laptop isnt going to handle DVD or even video very well its just too slow. GPS probably but your going to have to get some ram in there.
Start up shutdown on a laptop, an opus or any power supply the same as that just isnt going to work as they are ATX power supplies. The battery idea will work but your going to have to open the case up and solder connections onto the power switch of the laptop. You will then either have to use a manual switch or build a circuit to pulse on these connection. Have a search there is a circuit in here somewhere to do it. Alternatively you can make a fake UPS again search for the circuit. Old laptops might be the cheap solution but they are far from the best and for your furst time round will complicate things a lot.