If we are spiritual beings having a physical experience ...is there a limited number of spirits in heaven?

I disagree. I believe that the statement tries to put a limit on the limitless (universe) in more than one way. Not only does it say that the universe is finite by only having the capacity to create a limited number of souls, but it also detracts from the possibility that we may be incarnating elsewhere. True, there is no evidence to prove this but there is also no proof to negate it. The universe is infinite and limitless, and we being part of it, are also.