Starting a repair business - What do I need to know?

Hi,

I want to start a repair business. I have repaired a couple phones.

There are a lot of tutorials on the internet, but they don't really tell everything I think?

Is there any good tutorial for me?

I have a couple questions like:

I buy lcd's, but if I want to test them, do I really need to buy every iPhone? Aren't there some lcd cables wich can convert the connectors to just 1 iPhone type?

And static electricity and those things, is that really a problem?

And how do you really know your LCD is broken? I have had a couple where I thought they were broken (crazy colors and everything) and a month later they just worked?

Does anyone have some tips for me?