I have just received my new RAID device, and am going to start moving stuff from internal HDD to it. My question is with regards to structure. Currently I have a folder per system with each letter of the alphabet as a subfolder, and the each game as a subfolder with the respective letter. This works ok, but I am considering other structures. One which appeals to me is to have a list of alphabet letters, and then from there have game name plus release year, and within that a subfolder for each system, where needed, ie no point keeping an emulated Amiga game if I have a pc release. So this structure would help with duplication.
I am wondering if anyone else does this, and has thier own thoughts on this? Note its not necessarily a game in the folder, it could be patches, or docs, mods etc, and I can deal with that in subfolders, but still need a generic main structure.

I currently have almost no system. Or I have had multiple systems, changing over time.

For a while, I had <OS>/<games|applications>/<software name+CPU architecture, where applicable>/..., whereas now it's pretty much <store>/<game title>/...

CPU architecture was/is mostly applicable to old Macintosh software that may be 68k (until 1999) or PPC (1993-2007 or so), and since 2006, x86.

I don't have enough storage space in one location to neatly organise everything at the moment, so drives from before my switch to Linux use the old system, and what little I have downloaded since use the new. I don't really know how I will organise it later.

And yeah, I keep copies for all systems they're available for (assuming I have a copy for the system), regardless of whether or not I currently have said system - I may acquire such a machine in the future and want to use the software on it just because I can.

Yes, I had the same issue some years back. At that point I got a hot swappable drive tray in the machine and 4 * 4tb HDDs, some onsite some offsite, and I have been rotating them for some years now. But I started getting close to the 4tb - pics, music, films, games etc. So I thought for my BDay I would splash out, and got myself a terramaster four bay and 3 6tb red's. Raid 5 gives just under 12tb! So that should keep me going for several years, and with the possibilty of changes to storage medium coming up this year (I saw a post for a 15tb SSD!) no point going bigger.

I do need to organise a fair few things though not just game related, but calibre does books, and music bee does music. Am in half a mind to write a small application to do a simliar thing for games, but need to get some base underlying structure first. Not sure I need to worry to much other than system game title - unless there is reasons? So my current thinking is either what i have:
<system><list of alphabet><game name><subfolders>
Or:
<list of alphabet><game name [year]><system><subfolders>
Main metadata would reside in root, then each game name would have its own metadata. I already have spreadsheets with a fair bit of metadata, now I just need to stop play Grim Dawn for long enough to figure it all out :o)