is there a maximum number for pojos that can be included in a single package

I dont think so.
As hibernate is strictly following ?JAVA? syntax, there is no restriction on numbers of classes in the same Package, hence not on POJOs either.

ok the question in another way
how many classes the session factory can load(from hibernate.cfg.xml) to still performing will

There is no answer. It all depends on your POJOs, what you are doing with them, your available memory, disk space, number of processors, which database you are using and probably lot of other things.