Well, that IS expensive. Seriously

Some months ago I would have sent you my price list, but we just threw out all hosting customers - no money in it.
Anyhow, Ninja WILL crash with memory. You can not safely throw more than 3gb RAM at win32 for Ninja, and Ninja will happily use only 2 of that (limitation 32 bit process under normal Windows - 2gb for the program, 2 for the kernel). This can be changed to 3:1 (3gb for the program, 1 for the kernel) with a startup parameter during boot), but this is in "no supported" area for Ninja.
And, to make things better: forget about uptime in that context. The VPS host will gladly give you high uptime (my own servers calculate uptime in "how long until I needed to patch", which, from the SERVER side (using WIndows Hyper-V on a core install) is calculated in many many months by now (lots of patches, but rarely one for srever core requiring a restart).
Sadly, that wont help you. Ninja-Trader (6.5) will still happily crash every other day. Point. Bad memory management in the application. Which the VPS host wont even see. I strongly suggest daily restarts, minimum (of the application, not the operating system). When I log into my (currently remote running on a virtual server) trading system using remote desktop, I prety often have (after weekends) a nicely stuck and frozen uder interface presented by Ninja Trader
Or wait for Ninja 7 - I mean, you are not the only to complain, and supposedly Ninja 7 (beta out end of June) has a MUCh better memory management. Otherwise

well, I will not bear with it

And many others neither.
But until then nothing, sadly, will give you good uptime in Ninja.