A1: Yes, you can specify the date range you want to sync within the PDA Sync Wizard, but it is generally not necessary to do so. Logbook Pro
remembers the last time sync'd and will sync from that point forward on subsquent syncs. In my opinion, it is best to sync after each rotation, that way if your PDA gets lost, damanged, battery dies completely, etc your data is already safely in Logbook Pro.
A2: Data is not purged from APDL during the sync process and remains on the device for later review. APDL is a replacement for your little red/black book and can be used as a standalone product. However, the only way to export data and create reports from it, is by syncing to Logbook Pro.