Hi
I own computer shops which do repairs....
There are a LOT more than 10.... as an example you NEED every single version of Windows from XP onwards to 7.... so with 7 as your example, you need Home premium, Professional, and Ultimate and in BOTh 32 bit and 64 bit for each...thats 6 discs ...same for Vista and XP....and they MUST all be legal discs....
Then lots of other diagnostic stuff.....
But as already said, if you dont know this already, go into ANOTHER business....
One final thing,,,,,make sure you have Insurance and Legal cover as sooner or later one of your customers WILL take you to court, even if its not your fault....
All the best Brett