Fair enough, I've compiled it on Centos 6.4 but to my surprise it's now using all RAM and half my CPU and on its merry way to eat through 7gig of storage.
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- if I push it to a small VPS (say 512mb of ram), will it just fail (ie, do I need 4GB+ RAM)
It doesn't use much CPU once it has finished synchronizing with the network. Memory usage is about 300mbytes for a non-listening node, make sure you don't confuse virt (address space usage) with res. A 512mb vps is a little cramped, and you won't be able to compile it on it most likely.
Running a full node is the gold standard for node security. What security needs depends on the peculiars of what you're doing. If you're only sending funds to yourself (as you seem to describe!) then you don't have much security requirements (but then again, if you really were doing that you shouldn't be transacting at all).
I would strongly suggest you think very carefully about using VPSes if you'll be holding a non-trivial amount of funds. Anyone involved in the operation of your VPS service could scan the disks and steal your private keys. There has been at least one high profile case where someone used a backdoor in a provider's management infrastructure to rob a bunch of coins stored on typical-security hosting.
