With regard to the serial numbers, it really doesn't matter to the program if there are numbers missing between records in the database. What is important is that the remaining numbers be unique and cannot be changed. The ID field is there to, not matter what else is going on the the data fields, to be the one constant unique field for that identifying the record. That said there are certain business rules that require that the serial numbers be sequential or that deleted records are accounted for, so that is between you and your boss.
If I read your question correctly, you don't really clear the records, rather you create a new record with blank fields. There have been a number of threads on this forum in the past few days on record locking. This is a technique to set a field in the record that, based on the privilege set of the user, won't allow the data to be changed. Search for "record locking". This sounds a bit complicated, but it is a good way to learn about FileMaker's Security management options.
And you can look up more info in FileMaker help as well on this subject: See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis".