I had a African tank for about ten years , but things got in the way so I have been absent for about 30 years. I lost my wife of 61 years and now I have time.
Will turn 84 in a month and need a little advice as I have forgot some things about the art of fish keeping.
Welcome fellow old time fish keeper.
Sorry to hear of your loss.
I've been at it for over 54 years now and was in the fish business for 45 years so I have a good knowledge of what was and what is now. A lot has changed in the past 30 years. Many fish species are now farm raised vs wild. Sadly, many farm raised fish do not have the vigor or longevity of the fish from the past. Long term expectations should be tempered. Things today is not the same as years past.
In many areas, big box stores are more the norm than the Mom & Pop shops. If you have a good Mom & Pop shop locally, I suggest you support them. You may pay a little more for your fish and supplies but you get what you pay for.
The good news is that there are now more varieties of fish available as many species have been discovered in the past 20+ years from the Amazon as well as Asia/ Eurasia so the chances of working with something "new" is high, especially from a Mom & Pop shop.
As for the actual fish keeping, what we now call " Cycling" was what we called " establishing" a new tank. This is the process of establishing a bacteria bed in the tank and filter ( this "bed" is oxygen dependent so areas in the tank with the higher oxygen levels will have a more robust
bacteria bed. This is usually in the filter or areas where there is high water flow. ) This is a link to a simplified example of what's happening during the cycle:
https://www.aquariumcoop.com/blogs/aquarium/nitrogen-cycle
There are also products today on the market that are live bacteria cultures which you can add to your aquarium to speed up the whole cycling process. ( These are helpful but not mandatory as the bacteria bed will happen naturally. It just takes longer for it to happen naturally. ) You may remember an old product called Fritzyme #7 or #9. These were live bacteria cultures for cycling. The good news is that they are still available and in my opinion, still the best product for live cultures.
Diseases: There are a few more now than before. There have been some viruses that have been developed through the fish farms so certain fish like Dwarf Gouramis and some Angelfish have their own viruses that can spread to other fish of their family ( but not necessarily to every fish specie. ) Medications are now a little harder to get as well. Some of the best meds of 30 years ago are no longer available. This is why if you plan on purchasing fish on a continual basis, you may want to also set up a "quarantine tank" so that any new fish can be isolated from your main tank to observe for disease so that you don't get anything into your main tank. If you plan on a simple tank with only one specie, your main tank can also function as the quarantine tank. There is an old book called Handbook of fish diseases (
https://www.abebooks.com/book-search/title/handbook-fish-diseases/author/dieter-untergasser/ ) that has a wonderful flow chart method for diagnosing fish diseases. Since it is an older book, some of the medications it recommends are no longer available but once you know what you are dealing with, you can get what is currently available to treat it. This book is available on an number of online sites ( like Abe books, Ebay, Amazon, etc) and can be purchased at a reduced price used. Personally, the diagnostic charts in this book are worth the price of the book compared to the costs of replacing diseased fish.
So as you see, things are not all the same as they used to be.
From here, it's best for you to ask more specific questions and we'd be glad to answer them. Keep in mind that not all water is the same everywhere so knowing things like where you are located, your water's parameters, fish species you are interested in, your setup, etc will help us better advise.
Hope this helps.
