Was thinking a couple of PI's and couple of usb drives should be good enough to hang 100 folk off including a web interface.
Job done for 150 quid and an internet connection.
Are you serious ?
Have you not figured out in the world of IT that trying to do things on the cheap is only going to come back and bite you in the backside !
I honestly don't know where to start with your hair brained idea there are so many things bad with it.
If you are going to do it in-house, then do it properly. Otherwise outsource it somewhere where you get SLAs and someone else takes care of keeping the thing running for you.