Your room is approx. the size of our spare bedroom (11 x 14 x 8).
I have been able to successfully use flea and fly watt amps in that room, due to the volume, with a variety of speakers (some not associated with 3-8 watt amps).
If your interest is SET then keep things simple with a directly heated single ended triode design (DH/SET) most likely using 45, 2A3 or 300B tubes (approx. 2/3.5/8 watts).
There are other tube designs that also sound really good, but there is something special about DH/SET done decently that you have to hear to believe.
I would start with something like the Elekit and a pair of Audio Note AX2 stand mount speakers (now back in production I think) to start with if you can give up bass for awhile (add a sub, like one of the little Gallo's, later if you feel the need).
However, it’s not been clear to me if the Elekit amps are available with USA voltage power transformers (most I see are 100V).
I use good old production tubes in my inexpensive Bottlehead 2A3 amps (the tubes easily sell for more that the amps originally did), but I can still pick up a full set of NOS 2A3/12AT7’s for <$500 (I paid $60 for a similar set 20+ years ago;-).
As far as 300B’s go there seem to be quite a few well reviewed versions currently available and you do not have to pop for expensive WE’s or EL’s unless you want to.
WE’s 70’s production 300B’s were my 3rd favorite in my old Audion Silver Night amp as I much preferred Svetlana and then an inexpensive Chinese 300B to them (just a warning as to "What’s the Best" thinking).
I’ve grown accustomed to 2A3, but 300B is more power and a lot of Technicolor fun.
DeKay