There are plenty of ad networks but most of them are stagnant these days. No real advertisers. I would be more interested to see if you can get good advertisers on board.
Well, I'd have to pour some of my own funds after launch, to be able to attract quality advertising and quality publishers.
I've got plans on how to attract real advertisers, it's just going to be slow, but, I'm not rushing anywhere

We all have things we value.
Personally fill rate and speed are some of my pet peeves. Speed is mostly just a matter of equipment, but new ad networks often seem to have problems with the fill rate. Heck, even seasoned ad networks have problem with fill rates from what I can tell.
Id suggest adding functionality for backup ads, that way the publishers wont notice when you are out of ads to show.