The other point I need to determine is the database, wihch one to use? mysql or postgres? in the event that I need to cluster the DB aswell, which one is more fast/reliable?
What you describe sounds correct.
I'm assuming here the client for your SLSB is the web tier. Adding @Clustered to your SLSB allows the web tier to make calls on beans on another server. The benefit of this is if the bean is unavailable on the local machine, the web tier can still work. The downside is calls will be remote, therefore serialized. If your SLSB is going to have the same lifecycle as the web app (i.e. deployed as a unit), you're better of not using @Clustered and ensuring all calls remain in the same VM.
Great, thx for the answer, SLSB and the web tier will be deployed as a unit, so I wont get it @Clustered.
About the Entity Beans, performance sake they should be @Clustered, right?