The main concern I keep coming back to is that a person needs to keep their enthusiasm and interest. Debugging is a necessary part of this hobby, but if you start off with idiosyncratic approaches, there's a risk that you'll build a series of not-working or unreliable machines, and that leads to the risk that you'll give up.
I think this is a very valid concern but I seem to have done a poor job of explaining the approach I'd prefer to follow and why Garth's primer is not a good match for my approach. That doesn't mean it isn't an excellent resource or that I won't use it or try to understand sections of it; but it's unlikely to be my guide as I explore learning about the area.
So I'll try to do a better job of explaining how I prefer to learn things: it's fun to build things in tiny, tiny steps. Each time some baby step doesn't work it may require learning a thing all the way to the bottom, to understand it fully: but not every single thing needs to be learned up front.
Let me try with some examples: I'll start with yours, the need for decoupling capacitors. It's easy enough to discover that using three sizes of decoupling capacitors was standard practice at one time for each DIP and just start throwing on three capacitors at every chip - but this seems like a lot of work to do a thing one doesn't understand. If you build some simple circuits and put an oscilloscope on the pins to see what's going on and measure the difference between having long power leads to the chip vs having a small decoupling capacitor near by, it doesn't take long to measure what a huge difference the decoupling capacitor makes - nor to conclude that a single decoupling capacitor is sufficient. It's much more satisfying to learn it properly.
Still, I was able to build a "working" 6502 computer on breadboards with decoupling capacitors only on the power rails and not one per chip, validating the overall plan of what I'm building without needing to know about or understand about decoupling capacitors before I got started. That, ultimately, is what for me can help sustain my interest and perseverance: the ability to make progress without knowing everything in advance.
When the primer has as a prerequisite knowledge of all the 74-series chips that feels like a steep hill to climb when my actual circuits only need a few logic gates, mainly NAND gates, and perhaps a buffer. Do I really need to know about counters, synchronous counters, BCD decoders, BCD to seven-segment display chips, flip flops, 4 bit adders, shift registers, timers, and 64-bit memories? It seems to me simpler to focus on maybe the basic logic gates and buffers that I might want at first and learn about things like schmitt triggers and shift registers when I need them in my circuit (if ever).
When I say I don't understand AC circuits, it's because I don't understand how electrical force moves through space; I realize that changes in electric potential (voltage) create or collapse magnetic fields, and that moving magnetic fields induce current in neighbouring wires, but not why having a ground plane is sufficient to tame this problem while a twisted pair apparently is not. Learning how this works will wait until I have had a chance to verify that my build does not work at a frequency I care about, which several who know much more than I have assured me is the case; but once faced with a non-working computer at 1Mhz that works perfectly fine at a few khz, I'll have to dig in and understand it.
To attempt to summarize: what will keep me engaged is learning step by step what I need to know to add things to my system. The smaller these steps are the less likely that I will encounter a dead end that can't be understood and debugged. I thought it was pretty good progress to have a debug monitor that will show me the bus activity and disassembly of the running assembly in a week's time, and still feel interested in getting a serial interface going and attaching a keyboard and monitor all of which can be done without scaling the rather steep hill of how electrical force travels through space rather than through wires.
To me, setting aside time to learn everything in advance of building anything doesn't seem at all the right way to stay motivated and get things learned; learning enough to build a 6502 that can run at 20 Mhz seems unnecessary when there is so much fun to be had even at a few kilohertz.
