Cluster design: if I expect to insert data into several tables every week, is it a bad idea to cluster them?
I have yet to see a real world user scenario where the benefit (saving a bit of disk or I/O or block access) of using a cluster instead of just regular tables (or IOTs) with joins is so significant that it worths the hassle of dealing with it.
5-20 records per week: that is nothing. Paper and pencil can do that.
FYI: The data dictionary tables use a few clusters for identifiers. These identifiers never change. They are inserted, deleted, but never updated. In some environments, 5-20 records are inserted/deleted in a matter of seconds or minutes (due to dynamically creating and dropping objects) without causing any problem. So 5-20 records per week will not be a problem. The question is: do you really want to use something that is almost never used, that may not even improve performance noticeably (or even make it worse), but requires extra attention.