Mark you will find you only really need 2 or 3 sizes of collet because most small tooling comes with shank sizes larger than the cutter. Ie: 1mmDia will have 3mm shank.
You'll find 3 and 6mm collets will cover most of what you'll do with this machine form 1 to 6mm. 12.5mm collet or shank tooling you'll not use much with this machine. Maybe for surfacing but that's about it because it's not upto cutting with large cutters correctly.