How to...Free trial...

I am not sure that I like the fact that all users will use the same database. But I guess it is fine for the trial period, and if the client wants to continue, I can always transfer him to his own installation or something.

I guess it depends on your sales model.  Are you going to be selling this to a few large companies, maybe installing it on their servers?  In that case then maybe multiple databases makes sense.  Are you going to be selling (hopefully) to many different users/companies?  If so, you are probably going to want one database.