There is a maximum of 500 new sessions that can be created per minute, as referenced in this support article: https://support.logmeinrescue.com/rescue/help/is-there-a-limit-on-the-number-of-concurrent-rescue-se...
Current Rescue pricing can be found online here: https://www.logmeinrescue.com/pricing
I also suggest comparing the services of GoToAssist, in case this model fits your needs any better: https://get.gotoassist.com/remote-support/buy#/
We offer free trials for all LMI services, so you don't have to buy right away.
You can control the number of sessions each user can have at one time in a distributed session environment managed by the distributed session cache. The pdadmin policy set max-concurrent-web-sessions command specifies this maximum number of concurrent sessions.