[1] Go for a MT2 to ER25 or ER32 collet chuck, ER25 holds up to 16mm and ER32 holds up to 19mm.
With 4 collets 6-7, 9-10, 12-13 and 15 -16 you can hold 6mm, 10mm, 12mm and 16mm cutters also 1/42, 3/82, 1/2" and 5/8", either plain shank or threaded, so 4 collets hold 8 standard shanked cutters.

[2] Arc sells these. www.arceurotrade.co.uk

[3] Plenty of free CAD programs but the bit to convert to G code is called CAM and isn't usually free unless it's crap.
You will need to do a search, download demos and find one that suits what you want to do, the way you work and cost.

[4] No because by the time you can understand the jargon you are not a newbie lol