Yes, 150 to 300 is the limit for shared servers. Most servers have about 100 to 200 accounts on it. If an account requires more resources or CPU, you can upgrade it to be on a server with fewer accounts.
It's important to do this, so the server can stay strong in the case that several web hosting accounts burst their traffic or load levels at the same time. With too many accounts on one server, the server can slow down or even crash from this.
