What to say to someone starting an ad network...
You need to have a little luck and a good financial backer.
How to address the advertiser or publisher first question - answer is publisher first. Advertisers will not look at you unless you have traffic, and lots of it. To be a player, you should set a starting target of 150 million ad impressions per month. This will get you some interest from advertisers. To be a serious player, you should set a target of 1 billion impressions per month. In the online ad sales business, the more you have, the more it is worth.
But this is not the hardest part of owning an ad network. The real tough spot is operations overhead. Below are some of the costs:
: Ad serving technology - to be taking seriously, you will have to use a top tier serving platform $$$
: Server/Hosting costs - several dedicated computers to handle all the traffic $$$
: Personnel - sales, trafficing, accounting, developer, account manager, customer service to name a few positions
: Legal costs
If you want to be like Fastclick or Casale, then you are going to need a big fat wallet.
On the other hand, I think there are many possibilities for someone to start a niche ad network in let's say technology, gardening, etc. Then you wouldn't need the huge traffic numbers because you would have a desirable target.
All right that's enough. Just my two cents,