I'm sure the guys on here will give you a good estimate on what's a good amount of travel for a z axis (maybe start your own build thread? i'll be doing the same soon enough). I'm just a beginner on these things myself, so I'll leave it too someone more informed :).

The one I got off kip has about 115mm of travel, but I won't be using it all, because I simply will never be milling that far.

I had the ballscrew on ebay for £50, but no one was interested, so I guess I'll take £45 for it. After all a new ballnut alone from Zapp is that much, and it is new. Single nut.

I like the design on your router, but again... I'm just a beginner. I'm using linear rails now myself, and I do like :). My bank balance doesn't though :)

Also, by the looks of it your going to use some square alu tube for the frame? I suppose it depends on what tools you have available to you, but you might want to consider aluminium extrusion frame? I decided to go down that route after making a complete mess of the alu tube. It was alright, but I was never going to be able to make it accurate enough with just a hand drill.