The X1 is not a good candidate for CNC because it will always be a light duty, slow cutting machine. It is not rigid enough for serious work and most people who CNC it outgrow it quickly. Even if you ponied up the $3500 to buy (Just a souped up X1) one of THESE:
http://littlemachineshop.com/product...3501&category=
it would still suffer from those limitations.
That being said, if you insist on throwing your money away, the BEST mod you could make would be a belt conversion, or else you will soon be awash in white fluff from destroyed plastic gears.
http://littlemachineshop.com/product...3488&category=
Your micro mill comes with a metric drawbar that will only ever fit the supplied chuck. In order to use standard 2MT tooling, you will need to buy this drawbar:
http://littlemachineshop.com/product...2034&category=
You could also go to Lowes/Home Depot and just buy a 3/8 x 16 bolt of the same length--This will work fine.
To do any machining at all, you will need a set of end mill holders:
http://littlemachineshop.com/product...1978&category=
Or at LEAST this 3/8 end mill holder:
http://littlemachineshop.com/product...1705&category=
and of course, some same-shank end mills:
http://littlemachineshop.com/product...1242&category=
CR.