Requests to the server (installing Mediawiki)
The number of users is not sufficient to speak about the requirements, it’s mainly the mean number of active users which is important (1 active, 10 active, 100 active?), where "active" could mean "edit once a day". An out-of-the-box MW is not very demanding in ressources for a small wiki (tens of edits daily), typically on my unoptimized laptop pages are loaded in half a second (no other user but me), and you will have to optimize Apache, MySQL and PHP to get good response time. BlueSpice could be more demanding, but I didn’t installed it. If you have hundred or thousands edits daily, you need a more powerful server and look at caching systems (see documentation). For disk storage, you need some hundreds of MB for 10 users for 1 year (I think, experience from a small public wiki using only image files), and is mainly depending of the mean number of active users and your usage of the files (is it an archiving wiki with many files or just for some images/documents sometimes?).