You need a CNC to make a CNC.

[Zeeflyboy]

1.The design i have based mine up uses a bearing block that takes a '6207' bearing.
i would like to replace these with a standard of the shelf part so means less machining again.
Thsi is what he makes...sure there would be an off the shelf soulution

You would be looking for "FK" type blocks for the fixed end (proper ones will be using two opposite facing angular contact bearings) and "FF" for the floating end. You just have to choose the correct size to suit the machined ends of your ballscrew.

2.Helps on the X axis understanding what slide/block is needed to link the 'Leadscrew' to the sledge. (as it where)this would help finalise hole placement on the lower part.

Depends on the size of ballscrew and the type of nut. If using 16mm and a "normal" flange type nut, then something like an HD16 - ball nut is attached to that, and that gives you a mounting surface.

3.if using 'Mikeyc38' X Y axis need to under stand how the motor would be mounted and interact with the lead screw.

Don't really get what you are asking there... looks very simple, motor bolts to mounting plate, pulleys connect shaft of motor to ballscrew through a timing belt. What's to understand?

3.understanding what pulleys and belts are needed.

Technically none... you can direct drive the ball screws if you prefer. Advantage of pulleys is that it isolates the motors from vibration more effectively, disadvantage is that you are introducing a tiny amount of flex and another potential source of backlash.

If using pulleys, a nice chunky HTD type belt is a safe bet... https://www.bearingboys.co.uk/Metric...lts-HTD-1214-c

4.understanding what ball/leadscrews are needed.

1605 or 1610 ball screws would probably be the best bet depending on whether you are going to gear down with pulleys. C7 grade would probably suffice. You can get your own ball screws machined up to your requirements but you might be better off finding some suitable "standard" type screws that give your desired work envelope and design your machine to fit them as it keeps things cheaper.

burnign question also is it just worth buying a kit machine of internet? (convenience etc etc etc)

Depends, half the fun can be in building your own machine in the first place.