Tube cost and tube life (which depends on the amp design) are the sort of factors that would influence your decision on what to build (or buy) yourself.
Phil, keep those articles handy to cross reference any other reading against. Yes, they're a lot to chew on, but they pull no punches and aren't trying to sell you anything. They are just a reductive description of how these devices work. They make for a handy BS detector, and there is unfortunately a lot of BS out there in tube land. Re-read them a couple times until it sinks in. Poke around the other articles at that site, as they will help fill in the blanks in your understanding. I'm not trying to discourage you from going into the tube zone (and neither is the author, who admits to being a fan of tubes), just that you go in with your eyes wide open if you do.