Modding Reps | Link to sites | Gen Rolex parts

I see a lot of people posting a modded rep. Sometimes I question why they would do this but then again, I can appreciate the effort put in. I myself love Subaru's and can’t seem to keep them stock, so why would I keep a watch stock? I'm aware that you can buy Rolex parts of eBay but I'm not always confident about fitment and I sure don’t want to waste $400 on a part for nothin'. Can someone guide me to sites where I can buy Gen Rolex parts? What are some of the first upgrades that should be done? When does the cost of modds reach a point where buying a Gen was the better option, lol?