There are no specific recommendations for the sizing of View Composer or the Event Database in the 4.5 documentation.
That being said, the View Composer database will not be growing to a ridiculously large size. It hold some specific info about each replica and each linked clone but there will be a max of 5-6 (approximate) records for each one of these in the database for even if you have several thousand desktops (max of 3000 VMs in vCenter currently) you will only be looking in the vicinity of 20000-30000 records. Not too big.
The event database is a bit different as it will hold all historical events of your View Brokers so over time it could get quite large. I haven't seen any specific guides as to how large to make it but it also shouldn't grow at a large rate unless there is a problem which causes thousands of events to be raised or if you have a gigantic Non-persistent (floating) environment that is creating and destroying VMs like crazy.
Sorry I can't be more helpful right now!!!
-Mike
Twitter: @MikeBarnett_
