How can I set the maximum number of processes?
I don't know of any way to limit the processes. Importing is a large task since it's hitting so many fields, tables, etc. That means a lot of processes regardless of how many records you're importing. Shared servers often times have too low of limits to be able to fully use CiviCRM without running into issues. It's why we finally ended up just getting our own server, setting it up so that its minimums would still be more than enough for Civi, and then using it for all our sites.