Advice for newbie on Tube gear

I'm seriously condsidering getting into tubes (valves here in UK).
I saw & heard them once at a hifi show & have been fantasising ever since.
I'm a bit tech illiterate.
I've been offered Sonic Frontiers SFL-2 preamp + SFCD-1 CD player (240V) for US$2200. Cond is v.good, tubes are about 18mths old. I'll probably buy an ss power amp also(below $700 used).
I'd appreciate any advice on what I'm letting myself in for :
How difficult is it to find & change tubes , How will I know when tubes need to be changed , How much will it cost , What else will I need to do (biasing???, capacitor replacing...).
Are tube SF units low maintenance? I don't really have much spare time ,and am easily confused by techy things.
My system : nothing left apart from AQ Diamond X3 i/c's, AQ Sterling spkr cable, and an old pair of excellent highly sensitive (96db), hi-end(ish) French speakers - Helius Sirius II (only a few made in the '70s/'80s).