Brakes - Discs and pads

[Als_Zetec]

Howdy doody all

a cursory glance at the discs and pads on my WP Zetec reveals that it's probably time for a replacement. The original set have seen me through for near on 90K km and I'm quite happy with that.

A couple of obvious questions arise though, and I'm sure that there are obvious answers...
1. Can the discs be machined?
2. If so, is it worthwhile?
3. What is the minimum disc thickness?
4. Can anyone recommend good aftermarket discs to use? Factors are improved braking without harshness, disc / pad life and cost.

As a side note, I am going to try either Ferrodo or EBC Greenstuff pads.

Cheers

Ali.