You guys have it all wrong. This is a hobby - not something that you would do to make a living. I suppose if you were an early adopter and you saved your BTC then you could retire early (some people who joined early got a bunch of BTC, so they are sitting on a couple hundred thousand USD), but now it is nothing more than something that will help you kill time. The total time I've spent on this? A lot. Maybe 100 hours. Maybe more. How much do I stand to make? Each of us will probably walk away with $200+ pure profit. We put about $600 total in to it in the beginning, and once we sell off our hardware we should end up with at least $1200. So that works out to $200/person. Certainly not a lot of money, but enough to cover the cost of upgrading a few computer components. And I learned all about Linux while doing it (had very little experience before) and I am using it to make my first trading algo (had no previous coding experience at all), so while I have only made maybe $200 it has been well worth it in my opinion.
Once we got the miners set up and running, there wasn't much invested time after that. You just need to check them every once in a while to make sure they didn't randomly crash. A normal person who didn't have a lot of time on their hands could easily invest just 2 hours per week into this and be fine.
I use the MtGox exchange, but I wish you the best of luck with yours. If your fees are low, I'm sure you will get plenty of business. I would probably be willing to test it out for you. What sets you apart from all of the other new exchanges popping up? How do you plan to steal business from MtGox, who obviously owns the market. My biggest advice for you is to keep your exchange professional. MtGox got lucky that they just became the default because IMO they don't even look that professional (though since the hacking they have certainly upped their game). A lot of the other exchanges don't look professional, and while I know that looks can be deceiving, if you delivered on a site that didn't look like it was going to steal my money, that would be a huge plus.