There is no practical limit to the number of LPR queues that can be defined in Workflow, but after a couple of hundreds the display in the Configuration Tool will probably start lagging a bit (this has no impact on the Workflow service).
However, since a LPR queue can be defined with a dynamic address, users who have several hundred printers will usually only create a few queues and let each process set the IP address of the actual device they want to send each job to. This makes it much easier to manage and saves you the pain of having to manually add hundreds of printer queues to the Workflow Configuration tool.
As for the Workflow preferences, there is no “simultaneous print jobs” setting. What you have is a maximum number of replicated processes, which may or may not be print processes, or which can each print to several different devices.
I would suggest that this value be set to the average number of jobs that are being processed by Workflow at any given moment during the day. Once you have set that value, then you must set each process’ share of that maximum, which is defined as a percentage of the total value in each process’ Properties.
If a process handles a large amount of small jobs, it should be set to use a higher percentage of the total number of replicated processes.