I came back in after a hiatus about ten years ago. I did a refresher and was fine. It depends a bit on what type of diving you want to do. If you have an AOW card from back in the day, you can ease yourself back into diving without spending on the classes. Read, find some buddies that you can work with. If you have a pre-AOW certification, getting on charters will be pain in the ass.
The old tanks aren’t really worth keeping unless they are steel. Many shops will not service old AL tanks. I expect you already have an idea of what type diving you want to do. I got Nitrox certified for dive travel, but never use it locally, because I don’t really get a significant benefit when I am doing two tank in a day on my one day off.
Computers are a super improvement over tables, but a basic computer will do pretty much everything an expensive computer will do if you are staying within the NDL. I had an air integrated computer and it was really nice, but when it died, I bought a replacement that wasn’t and I don’t miss it that much. It comes down to type of diving (needs) and budget. Scuba Board tends to swing tech,