Hi mate,
Shouldnt really matter what colour you go for as all paint is the same to put on. I mix all my own colours but if i were you id be looking at expresspaints.co.uk,paints4u.com. I use standox paint mainly and i swear by it.
The finish is all in the prep work, personally i wouldnt sand it to bare metal unless it was a show car or you were restoring it etc.
You can do a full colour change by just 'scotch brite'ing' the whole car down (like a brilo pad that takes the top layer of paint off) or sand the whole car down wth 300grit sandpaper, just remember if you are doing any filler repairs to filler primer them and sand the filler primer down before you start to paint it (also its best to leave the primer over night if painting over filler as the filler absorbs it and you will see all the filler repairs through the paint).
Make sure you clean it all well before you start painting, i use panel wipe but you can use thinners.
If you want a mint glass like finish, get a good few coats of laquer on then when its dried sand the whole car down with 2000wet and dry (wet) just until the paint work goes dull, then machine polish with Farecla G3 or 3M cutting compound and it will take any imperfections from the laquer and give a tottaly smooth finish to the paint and when polished up gives a glass like finish