it's been years since i did this but i used to position myself as such. it's quite comfy but it causes mild neck pain after a few hours. alternatively, lay on your stomach, place a pillow on your stomach to arch your back properly, and a second pillow near your face. that way your neck isn't messed up.

I do it all the time. It doesn't that requires much thought, just get yourself into a natural-feeling comfy position. You probably want a lower-power machine as the heat is annoying and the computer will tend to overheat due to exposure to body heat when you rest it on your body, and the vents getting blocked which happens whether it's on you or the sheets. Alternatively you could use some sort of table setup, there are little tables that can roll over the bed, that you could use. But it's not really needed.

long wired mouse and onscreen keyboard