Any thing is doable if the funds are there.
X-Axis and Y-Axis:
I have yet to see a drawer slide that long.
Gas pipe with bearings- least expensive, accuracy-ok
Round linear bearings(supported)- moderately expensive, accuracy- better
"THK" style rail/bearings- expensive, accuracy- best
Double Vee rail/bearings- expensive, accuracy- best
Z-axis:
I would go with either the round linear or the THK style due to the short length.
Only your imagination will determine the length. The gas pipe idea can be gotten thru the hardware store. The round linear and THK idea is best gotten thru Ebay. The Double Vee rail must be gotten thru the mfgr. or a bearing dealer.
Stepper Motors:
Torque equals speed to a point. I would start out with at least 450 oz. of torque. Due to the lenght of your x-axis (8 feet), a ballscrew would almost be cost prohibitive for a home machine. You would be looking at a rack and pinion or a timing belt for a drive. You would have to gear down your motor to make either one of these to work. By doing so you would increase your torque but lessen your speed. To get your speed back up, bigger motor. Bigger motor, less gear reduction. Oh what cycle. Increasing voltage to the motor will also speed things up---to a point---
Your Y-axis could be driven by a ballscrew due to it's length with no problem.
Routers:
Everybody seems to have thier favorite brand but Porter-Cable routers seem to be the going thing right now, the bigger the better. They can be found at local hardware stores to specialty wood working stores.
Software:
I can't comment on that because there are so many out there. It all depends on what you want it to do and will the program fill your needs.
If it's not nailed down, it's mine.
If I can pry it loose, it's not nailed down.