We're unexplained as well, and our FS also gave us a 50% chance of our first cycle working. And here we are planning our fourth stim cycle...

Funnily enough, after 3 failed stim cycles (and 1 failed FET) I got pg naturally last month (first ever bfp after almost 3 years of TTC!), but we lost it very early. But I'm hoping this means we do have a chance of IVF#4 succeeding!

As for the number you can/should do - that's entirely up to you! Try not to think that far ahead. Hopefully the first one is the only one you will need. If it doesn't work, that's when you ask yourself if you want to do another and when you want to do it.