Maintenance Planning PM Projections-when and how often?

We are using 9.2.  I have set up and tested through each piece of the Maintenance Planning process.  Everything is working fine, we have the inventory item number and parts and routing attached where needed, the PM Schedule and everything works fine all the way through to generating POs.

Now that we are putting it into production, I have a question about the timing of the process as a whole.  

The projections/forecast will be generated even if there is not a PM WO created yet, correct?  So I'm assuming it doesn't matter when we create our PM's through R12807.

We do, however, run MRP for these items every day. Is it common practice to update PM Projections every day in a scheduler so that your MRP has the most updated forecast?   We plan on doing this planning piece only for 6 month or 12 month PMs, so is it better to only generate projections on only those serial numbers (data selection),  or is it better to make sure that ONLY our Inventory Item Number on our Model WO includes a BOM, and just run it wide open?  Although it will run longer for sure.