Profiler says that memory usage of one average page is:MIN 587.9219 kB - MAX 1,942.9219 kB - AVG 1,059.7098 kBIs it possible to guess how much memory I should buy to a server? There could be ~1000 simultaneous users.

2MB * 1000 users = 2GB :)
Or just get 8GB+ since it's dirt cheap and don't worry about it.
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