About #2 - get a chair you are comfy in. Don't buy the most expensive, most hyped thingy everyone says you need, feel your own body to decide.
Different people got different needs for sitting.
Oh, and if you do anything where you have to work a lot at a computer, for heavens sake get a decent screen.
Buying a cheap tft will give you a headache, kill your eyesight, even though you can't spot the difference.