... it might lead to the need for a scope.
An oscilloscope is absolutely essential if you are to make any progress as an electronics hobbyist.
An EICO 460K oscilloscope kit was my second purchase, as a teenager, after building an RCA Voltohmyst WV-77E VTVM (Vacuum Tube Volt Meter), also from a kit. These two instruments truly got me started down the path to becoming an electronics technician. By the time I graduated college with an electrical engineering degree in 1978 at age 34, both instruments had been replaced with more modern equivalents, but I still have fond memories of using them to learn and explore the fascinating world of vacuum tube electronics in the 1960s.
Besides test equipment, you need to study and learn electronics theory if you ever expect to progress beyond "monkey see, monkey do" assembly of cheap Chinese copies of OPDs (Other People's Designs). I think the only thing you will learn from that is it is very easy to get ripped off by Asian vendors.
Caveat emptor!
There are some bargains to be found, but you really have to know what you are doing before tossing money at them. Even then there is no guarantee you won't get ripped off by counterfeit parts and other components of questionable quality. For example, look closely at the "standard" transformer you are considering using, especially the manner in which the windings are "scramble wound" on separate halves of the nylon bobbin, and how the bobbin is inserted on the core of the transformer. This is not a quality part, although it may be serviceable for some applications. But how would you know that? The specs are "subject to change without notice!"
It is easy to find a quality transformer from any of several reputable electronics distributors. And there is usually a link to a PDF file with complete specifications on their web page. Being retired and trying to survive on a limited, fixed, income may make the Asian offers seem like a God-send. Maybe so, because you WILL learn something from the experience of buying from them. Me, I would just as soon pay a little extra (sometimes a LOT extra) to get parts that I know are reliable and will meet their published specifications, instead of trying to obtain a refund on Asian junk or, worse, just writing off the loss to experience gained.
I too am now "retired, living on a fixed income" but over the years I have accumulated a lot of quality electronics parts. That means I only have to purchase "new stuff" to try to stay current with technology, and today the "new stuff" is incredibly cheap compared to what electronics used to cost. Not all of it is cheap Asian junk either. Some of it is cheap, but serviceable, and happens to be made in Asia. The trick is learning how to determine the difference, but hopefully not through bad experiences. Google and various electronics forums are your friends here. Learn from the experience of others.