With jBPM 5.x, I couldn't found information about about use in production enviroment (real life) and best practices. Decisions about use, for example create a new session per process instances, or use some session for multiple process instances, impact in two ways (there are lots I suppose, I'm not an expert in drools and jBPM).
1) How you write rules:
In the rules you must write carefully when you create multiple process with some session, becouse you can write a rule thinking that impact in one process instances, and in reallity impact in more than one
In don't have time to do stress test to verify how impact use one session per instances. In this way, you have multiple small sessions, but you access more times to database than use one session in memory.
I except some more experience user of jBPM write best contribuition to the community. This things are very important. But, as opposite, is a free product, so if you pay support you will have answer your questions.
PD: Sorry my english