I promise I will stop asking daft question soon. Ish.

[Jonathan]

As far as the ballscrews go, would a 20mm 5mm lead not offer better accuracy, I'm not intending to do large volume runs of stuff so speed isn't that important (as long as it doesn't case any material problems) but precision for engraving is.

Yes, but overall you're still better off getting 10mm pitch ballscrews since you can use pulleys and have a 1:2 (motor:ballscrew) ratio to get the same resolution as a 5mm pitch screw on 1:1. If you got 5mm pitch then the ballscrew has to spin twice as fast, so unless the critical speed is twice as great you will be limited. The critical speed is just proportional to the diameter, so using 20mm will only gain 25% speed hence there's no point. If the 20mm diameter screw was 10mm pitch I probably still wouldn't use it since the required torque to accelerate it is much greater.

Also the resolution you get from 5mm pitch is hardly ever required. I cut this with (roughly) 10mm effective pitch:

The area shown in that image is roughly 50mm wide...

online resource for explaining the basic maths and mechanics for working this stuff out properly so I can stop vaguely throwing combinations of parts around in the hope that someone will work it out for me? :)
... preferably with emc2 examples?

Er, me? But seriously, the information on this forum is all you need. If you've not already then read as many of the build logs as you can as the same things come up regularly, so it shouldn't take long to find out what the best way to each part is. The fact you're intending to use LinuxCNC doesn't make a lot of difference to the process - in most cases it'll be just selecting a different option when you export the G-code from the CAM program.