What you are describing sounds about right for what your VPS should be able to handle. The most basic vShare site (little to no traffic) would be fine on that type of VPS. For anything else, you will need at least 1GB minimum of dedicated RAM. For serious sites, no less than 8GB of RAM. CPU also plays a part in this as well. The biggest load is going to come from mySQL so having plenty of RAM and CPU is essential.