I'm afraid my only recommendation is not immediately useful, which is to start reading/skimming a 1,000 page book, Practical Unix & Internet Security, 3rd Edition by Simson Garfinkel et. al. (http://www.amazon.com/Practical-Unix-Internet-Security-3rd/d...).
But's that reference is only "a mile wide and an inch deep* (from the Amazon.com reviews).
How much time do you have? How much flexibility in choosing your OS (e.g. is OpenBSD or a Linux that really implements SELinux an option)?
And there are so many details today, like how do you get adequate entropy for your RNG on a VPS?
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