Adbrite and Adsense can coexist concurrently on the same site. But please make sure that you are not subscribing "Interstitials" ads under Adbrite. If "Interstitials" ads being included, it violate Adsense TOS.
I don't understand why build 50 sites when you can have 4-5 make them good and stable and afther that when you have money to invest and if you have ideas expand ... I can't say mutch about adsense now as i only have it on my webdirectory not earning very much but i'm preparing 4 sites to put on the web will see then how it works .
yea i love the idea make only one and make it spread like virus you could get more than $10,000 with just one site
Why have 5 sites when you can have 50? Just keep adding sites to your inventory. The sky's the limit.
Personally, I like a mix of small sites, and big sites with many pages. Large sites are easier to manage and administer than a large collection of small sites. Here's a nice calculator that can help figure it out. www.stackpoint.com/adsense_calculator (sorry I'm not allowed live links yet)
You can have USD$300 daily using Adsense. But you must have an enourmous traffic to accomodate that conversion.