Note that you can probably lower the CPU cores and RAM a bit. Multiple JVBs of 4 or 8 cores with, say, 8 GB RAM work much better than one monster JVB, and JVB won’t use all that RAM anyway. With multiple servers you will probably get more bandwidth from your provider too.
VPS have a GigaBit vNIC - so bandwith is up to 1 Gbit/s
I wouldn’t assume that. If you’re not paying for a guaranteed 1 Gbit/s per server, you’ll likely hit shaping or congestion earlier, at least some of the time. Do some tests before your users test it for you