Cannyman,
I would always advise attending a recognised training course before working on a clients carpet, this way you will be well equiped to tackle a majority of problems you will inevitably come across. Equipment is also an important aspect, Hot water extraction cleaning will in 99% of cases be the system of choice, this along with all the other equipment needed will leave little change from 5k and thats if your carefull. Insurance and a sign written van will also take its toll on your bank account, then there is advertising which could be as much again
All quite daunting but well worth it in the long run

Paul