in customizing of the archiving object you define the size of an archive file, there are actually 2 alternative parameters, either by number of records or by MB.
Dependent on the selected data in an write job SAP writes 1 or more archives based on the above mentioned sizing.
Also depending on the customizing of the archiving object SAP either automatically starts the deletion jobs when the write jobs have finished or the write job just finishes without kicking the deletion jobs, then the user has to start the deletion from SARA menu.
If SAP starts the deletion jobs automatically then it creates as much jobs as archives have been written. Yes worst case they block all batch work processes.
if you start the deletion manually from SARA then you can select the archives for deletion and can schedule by yourself.
If you create smaller packages in the write job then you get more write jobs, but you can schedule them for different starting times.
At the very end you have in total probably the same number of deletion jobs, but based on the different schedule time for the write jobs they will not start all at the same time.