So the little feedback notwithstanding, I'll take a shot:
> 1 - does moodle have any issues being in a load balanced or cluster setup?
Load balancing Moodle is not trivial due to two things: the $moodledata file repository and the session data. This topic has been discussed many times in this forum. Run a search, for example
> 2 - What operating system is does moodle run the best on and why?
The one you master! Because it is the best for you.
I'm not joking. There is no absolute 'the best' anything. One is always looking for the best a) out of a given choice b) for a given situation c) for the person who is going to do it.
If you want to see examples of what those 'best' for other Moodlers were, you can search this forum for 'Windows Linux', 'Linux flavour', etc. You may be also interested in other flavours of Unix:*BSD, *Solaris, ... In the case of Windows look for 2003 and 2008 - and don't forget to get the openion of Windows people at "Windows-based servers" http://moodle.org/mod/forum/view.php?id=6799