Don’t put those on same VPS. It has tendency to break. It can be done and needs only a reverse proxy as Nginx, but…
500 visitors doesn’t need that much, but it depends how much you are dealing with files and are you using S3 or similar. But start smaller because increasing is quite easy. Take two general ones and 4 GB RAM for both. Amount of cores and HDD size is then what it is.
Or if you want to use one VPS you should choose at least 8 GB RAM.