3 IDENTICAL channels up front -- not two big "mains" and a ridiculously tiny "center." You need three of the same speaker up front
5. Surrounds identical to the front (or at least from the same family)
This isn't really necessary anymore. With DSP technology, I can have my A/V receiver match the rest of the speakers to any I pick as a reference. It's scary to hear how good it does, because the horn-loaded mains sound very different from the other speakers. I just have the system adjust everything to flat response, and it evens everything out.
All my surround speakers are matched, and I'll eventually match the front 3 to the rears, but it's not a priority right now.
All my audio gear is 10+ years old, some of it sourced from Craigslist.
How do you do multi-channel sound with hardware that doesn't understand any of the newer codecs? I know it's possible to run 7 analog cables from a device to the amp, but most amps have at most one such input. Even with in-device decoding and HDMI for PCM transport, I had to update to a A/V receiver with more HDMI inputs because many newer devices don't have any other output, and there's no way 10-year-old hardware will understand a new enough HDMI standard to work with new devices.
It takes commitment and a certain degree of crazy to make a proper home cinema.
I've been doing it for 28 years now (laserdisc & matrixed surround sound back then), so it's either become normal or is way past crazy.