Howdy Rex and welcome aboard.
Let’s hit those questions:
Yes that is more then enough bandwidth for the average portal, even if you feature free games for your visitors you should not have a problem.
This is a very tough question to answer and is wholly dependant upon the quality of your traffic, the casinos you are working with, the creatives you select, your presentation text and more…
Rather then raw number of visitors you will most likely look at other ratios to gauge your return on investment (ROI) and traffic value.
Ratios most of us use include:
Visitors/Download = Provides a simplified gauge of traffic quality
Download/Depositer = Helps you to locate casinos with superior credit card processing rates.
Visitors/Net Revenue = Establish your ultimate Cost Per Click for ad campaigns.
And there are a host of others in common use.
Hope this helps and good luck with your new portal…