When I started my diving training, I was just shy of my 59th birthday. I was a bit safety concious, and thought about redundancies. I used the gear list for PADI's Self Reliant, and SDI's Solo courses, to determine what gear I should buy, for my diving adventures. Before my OW even started, I had compiled all the gear from said kit lists. My 1st dive as a certified OW diver, I was slinging a 13cu pony, and I practised a switch over drill, while I flooded my mask.
I dove a lot, with my chosen LDS drop-in dives, but as a new diver, I sucked gas like a dragon. I would be down at depth with the group, and running out of air and someone, usually the DM for the dive, would "escort" me to the surface. In order for me to not shorten the dives of my buddies, a Solo cert was needed, so I could just surface by myself. Being solo certified, allowed me to surface by myself, while still diving within my certification. This was important for liability for my LDS. I did my AOW, 2 months after my OW. I started that course with 40 logged dives. I did the SDI Solo course, 11 months after I got my OW. I started that course, with 177 dives under my belt.
My only gear change I have undergone since I got my OW, was to upgrade my pony, from 13cu, to 30cu. I of course, have sellers regret for getting rid of the 13cu pony. This Sept will be the 3rd anniversary of me getting my OW, and I hope to be on my 400th dive fior my 3rd anniversary. So far, I have done numerous dives where I am just suracing by myself, or diving as a solo diver, but part of the "group" of divers. I have done around 30 dives totally solo, start to finish, and a handful of those dives, have been at night. My diving has all been coldwater, drysuit dives, in the Salish Sea, off Vancouver Island; where vis can be 1' in pudding like pea soup, to 100'+ in clear water. A lot of my buddies, dive self reliant, eliminating the need, to surface and look for your buddy, after a min of seperation.