How many sites on a hosting account?

The answer is it depends, it could just be just one depending on how much resources you consume:

Violations of the Terms of Service will waive the refund policy.
7a.) Resource Usage
User may not:
1) Use 25% or more of system resources for longer then 90 seconds. There are numerous activities that could cause such problems; these include: CGI scripts, FTP, PHP, HTTP, etc.
2) Run stand-alone, unattended server-side processes at any point in time on the server. This includes any and all daemons, such as IRCD.
3) Run any type of web spider or indexer (including Google Cash / AdSpy) on shared servers.
4) Run any software that interfaces with an IRC (Internet Relay Chat) network.
5) Run any bit torrent application, tracker, or client. You may link to legal torrents off-site, but may not host or store them on our shared servers.
6) Participate in any file-sharing/peer-to-peer activities
7) Run any gaming servers such as counter-strike, half-life, battlefield1942, etc
8) Run cron entries with intervals of less than 15 minutes.

Source: Web Hosting, Reseller Hosting, and Dedicated Website Hosting w/ cPanel - HostGator

Its a good idea to read the tos before doing business with a company.

I could only wish that I were cursed with so much traffic that they asked me to move to a dedicated host!

Regards,
PCRoger.