Thank you! Being a programmer, simulation is something I could actually manage quite easily :-) Yes, we're talking about anywhere from 2 to 20 random variables. The typical "click-rate" in my application is 1 click for every 1000 views, but this can vary from 1 in 10,000 to 1 in 100 - depending on the ad.

Ok, question completely re-written, would appreciate it if you could take a fresh look

I will attempt to rewrite the question to clarify.

Note, sorry if this question looks familiar, it is a reformulation of a question I asked yesterday, but which I realized contained a fundamental error, with some additions.