for a screen , I bought a pretty cheap led backlit lcd with touch without a frame , I am amazed by the sunlight readability
I know its Chinese but everything is Chinese :P , they do have good customer support
for fast boot times , depends on hardware but I find having windows 7 embedded helps a lot , also very easy to change the logon and bootscreens on that.
I say going for a motherboard with embedded cpu like atom dual core or amd e350 , something like that
also SSd are nice to have these days
Arduinos are in many different shapes and sizes , but they have different functionality like the amount of analog and digital ports
If you see my worklog you can see an example for arduino use, but basically if you have the patience and skill to work with them you can do almost everything with them.
My next idea is to use an analog port for the dimmer , when I turn on my lights the screen goes to night mode.