Tube amps - what 3 things…

If you don’t have huge power demands I’d recommend Dennis Had Inspire Fire Bottle KT88 SEP amp, and an Inspire LP 3.1 preamp. These products won’t break the bank, especially used, yet their performance is very difficult to top, especially at that price point. For $3k you can get outstanding sound for cheap compared to other products. I’ve had Inspire products since 2016, and happy to have discovered them. Audiogon is well aware of Inspire products!

I am not a EE and no where in the "Ralph" league but I would be careful of auto biasing.  I think it tends to suck the headroom out of tube amps.  Listen to Ralph and to ensure you don't end up with tube amp trying to sound like a solid state amp.

I am not a EE...

Please don't post myths. I can assure that autobiased amps don't suck the headroom out of amps. As long as the bias time constant is long enough, the speakers will be toast long before the autobias affects the gain... assuming you're not trying to drive 80dB speakers with a 20w amp.

Three things I would look for: 1. A sub out option. Some tube amps are sort of bare bones items but the sub out on mine really makes things convenient 2. Autobias feature. I was afraid of tubes due to the complexity compared to SS. If tubes can be plug and play it helps alot 3. Be darn sure your speaker efficiency matches the noise floor of your tube amp. A hyper efficient speaker (as in Klipsch Lascalas) can rake any hum or buzz out of any circuit. Depending on the volume and style of music played this could be an issue if you're OCD. Tubes by nature are noisy compared to their SS cousins. That said, tubes can create a sound beyond most SS i've ever heard (or could afford more like). I bought a Raven Audio Nighthawk since I'm a poor painter living above his means. I've really enjoyed getting over my "tube fear" and have been constantly amazed at the stunning realism it produces. My wife says the investment was well worth it. Never expected that!

My tube amps don't care if they're running 4 ohm or 8 ohm loads, have had both, and the 4 ohm loads do not cause any issues with greater loading, heating, etc, with the tube amps

I think you'll find that using a thermal imaging camera that on a 4 Ohm load, the output transformers are indeed running warmer.

I would be careful of auto biasing.  I think it tends to suck the headroom out of tube amps.

If you find this happening I would expect there's a problem in the circuit. Autobias shouldn't affect the power the amp makes.