Linear rail and ballscrew dimensioning for R/C router

Hi everyone!

I plan to build a CNC router to cut parts for R/C model airplanes which has been my primary hobby for many years. I am looking for advice on the selection of linear bearings and ballscrews. Any advice on the the dimensioning of these items would be greatly appreciated! First some facts about my project.

Working dimensions
Cutting area 1000 mm x 300 mm
Spindle vertical movement 100 mm

Materials I intend to cut
Balsa <-4 mm
Plywood <-4 mm (up to 6 mm would be a nice if possible)
Carbon fibre sheets <3 mm
Foam

Design
The design will be a box construction from MDF similar to this
Attachment 8549
DIY CNC Router for modelers - RC Groups

Motors and electronics
I have already ordered these stepper motors and controllers
http://www.ebay.co.uk/itm/German-Shi...00852051300%26

Linear bearings and ballscrews
Linear bearings and ballscrews will probably be ordered from linearmotionbearings
items in linearmotionbearings store on eBay!


X-axis

Supported linear rails SBR20-1200mm (2 supported rails+4 SBR20UU bearing blocks)
Ballscrews RM2005-1250mm-C7

Y-axis

Supported linear rails SBR16-400 (2 supported rails+4 SBR16UU bearing blocks)
Ballscrews RM1605-450 mm

Z-axis

Supported linear rails SBR16-300 (2 supported rails+4 SBR16UU bearing blocks)
Ballscrews RM1605-350 mm

1] Are 1200 mm supported rails for the x-axis to short for a cutting length of 1000 mm? I suppose that this depends on how wide the gantry base needs to be?

2] Is it correct to order the ballscrews slightly longer than the supported rails as I have seen in many of the sets available on Ebay?

3] Is the diameter of the rails and ballscrews roughly correct considering the length and the materials I intend to cut?

Thanks in advance!

,CNC