yes, renaming of CACHE.DAT to IRIS.DAT is supported, but not for the system manager databases.
Either just copy your own databases that way and recreate the required configuration (e.g. security), or - if you have a lot of config -, you can install Cache (into same directory path on new server), copy manager db (and cache.cpf) across and then do in-place upgrade to IRIS.
Is this going to be made available for on-demand viewing, e.g. on youtube?
You don't need to do it this way. Instead, get the id of the parent object and then, as you create each child object,
do childobj. <ParentPropertyName>SetObjectId(parentId)
and save the child object. That should solve your memory problems.
This is a technique that doesn't just apply to relationships but to any object property where you can avoid swizzling it into memory.
Log in or create a new account to continue