I keep a detailed file of my ammo on hand, which I literally do inventory on whenever I pack/unpack for a range day, or when I pick up ammo at the store.
In that same file is a list of each of my firearms and exactly how many rounds i've put through each of them. I do not keep a cleaning schedule because I clean them everytime I come home from the range.
I have digitized copies of all receipts and proof of sale etc, as well as all original paper copies. I store the files on an external hard drive with a back up to my CCTV system cloud which is maintained by me and only me. I run my own Server/NVR for my surveillance system at the house so I have no issues worrying about security as it's only available on my local intranet which can only be accessed through my Server/NVR. I keep that separate from my internet network.