Many great suggestions mentioned. I might suggest you watch Roger of Rogers High Fidelity YouTube videos on tube amps & what he feels are important. There are a few really good ones . He knows his stuff! Obviously, he’s also promoting his own brand but very worth it.
His offerings are relatively expensive but in his case, you get what you pay for. I have now for a year his EHF 200 Mark II integrated amp & it is outstanding! Very powerful w/great detailed beautiful tone w/ very good extension at both frequency extremes. It does run hot operating in full class A producing a true 100 watts + / channel but that’s the price you pay for that design & the sound quality it offers.
I’ve owned tube amps & preamps for 40 years; Conrad Johnson, Audio Research, Melos, New York Audio Labs, Art Audio & enjoyed them all. The build & sound quality of Rogers handily beats them all.
My thoughts on important aspects of a a tube amp are: 1- high quality, large power oversized transformers, 2- point to point wiring w/ good wire ( much easier to diagnose & repair should a problem occur) , 3- solid, non resonant physical construction w/ high quality input & speaker connectors.
enjoy the tubes! Warning once you go there, there may be no turning back.