Make sure whatever you set up has a conveniet bulk download option. Else it might border on predatory practice if the only option for your client to save their copies locally is to download every one of them individually.
Apart from that I don’t see any issues why you cpuldn’t supplement your income by offering hosti g services to your clients, as long as you can guarantee their data is secure and confidential and it isn’t too much of a hassle for you to manage that.
Darktable has a library management built in. Could help with automatically sortimg your photos by date into labeled folders. From there you can just start working on your backlog amd make sure to tag and maybe rate any new incoming photos in a timely manner so as not to add to that nacklog of work.