If I manually enter my transactions, will syncing my account create duplicates?
No, in general, sync will not create duplicates. Sync is smart enough to detect duplicates and automatically merge them, so you don't need to worry about it.
A synced transaction is considered a duplicate if all of the following conditions are met:
If you enter transactions manually in a "Pending" state. Upon syncing, they will be automatically marked as "Reconciled".