My wood floor support must have been built with green wood in 1951 housing boom after WWII.
Warp, dip near walls, flexible flyer.
My final solution, are the 2" x 2" iso-blocks, I wrapped them with black tape after this photo
amazon, easy return, try a type, no good, try another type.
They work well, but no dancing that end of the room.
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Hum is about the tonearm, not the spinner/plinth. No way would I use a 3 wire no ground wire system as someone described and as you have read about.
I always encourage finding a TT with the potential of two tonearms, start with one, add 2nd if/when desired.
Single arm, I highly encourage arm with removable headshell AND easy height adjustment.
Mechanics, my preference is heavy spinner, heavy plinth, direct drive
Nearly any TT with a cracked dust cover, thus less cost, can be an asset, as new covers are readily available, start with zero scuffs
sota, cracked lid, removable headshell
new dust cover, they can make one for nearly any TT
gotta start level, I made tapered runners each end of my rack
the shadow shows how the floor dips near the wall.
It also got me support a bit forward and a bit rearward of the rack, definitely helps stability