There is no direct correlation between hits/day/Bandwidth and memory usage.
free -m will show how much ram is in use. You should see little to no swap usage and some caching/buffers. It will always show 100% in use as free memory is used for caching over time.
The key is that you are not actively using swap. Once you are actively swapping out, the machine will slow to a crawl.
If your renting a VPS this may be a better question for your provider. They should have the technicians and access needed to make an informed recommendation.