IIRC, you can have around 20 concurrent connections and around 30 open processes. You’ll need to fit it all within the memory limits which seem to be about 90MB. I’m not sure if that’s per process (which would be very generous) or total across all processes and users. My guess is that it’s per process with a higher total limit for all users/processes in an account.
CPU time is basically as much as you like as long as you aren’t slowing down the server for everyone else. According to the wiki, this can be up to 300 CPU minutes per day, assuming your site is otherwise efficient.