The lip doesn't mean much, takes a few thousand miles to form. You need to measure the rotors thickness. Usualy you get two sets of pads out of a set of front rotors. Rear rotors and pads seem to last 100k-150k miles. Well unless you have traction control and give it a good work out, then much much less.
If you have no records of when they were last done, just replace them and get a base line. Rotors are cheap.