Little background about me:
Use to be a mold maker, changed gears and now I do rapid prototyping.
I own a couple of VMCs and Lathes, so I can build/make anything for this project.

Budget: $10k. + more if neccesary

Goal:
I'm looking into building a cnc router with tool changer that will cover 4'x8' material. This cnc router will be used in a production enviroment. Possibly be making signs, cabinets, 3d art.

Questions:
I've been doing alot reading on this forum and have some questions.

What kind of tollerances should I be expecting?
Whats a reasonable maximum feed rate for cutting 1/2 MDF?
3D contouring (xyz movements) feed rate?

Equipment Suggestions:
What type of linear guide would fit this budget? Fancy rack and pinion? Ballscrew (available in 8' length)?
Planing on using this router in a production type usage. What type of motor? servo/steeper? What size? Brand? Cost?
Table vaccum? cost?
Table: Extruded alumin stregth? Should I go with steel tubing instead? Flatness would be a concern.
Concerns:
I plan on also cutting 1/4" 6061 alumin. Is $10k a reasonable budget?
Since this is going to be a production machine; speed and accuracy is a major concern