I tiled 250 square metres in my villa in Spain...without kneepads I was tiling over the original floor tiles so everything was fairly level...I learned as I went along and was pretty good by the end! It didn't help that the two big lounges were circular...lots of cutting involved.
Back here in Blighty I've tiled my kitchen and conservatory floors with slate...tiles were very uneven but it's just perseverance and getting the adhesive mixed right that helps a lot. It's amazing how good they can look once grouted properly....just take your time.
To expand this is in my daughters house shes had an extension with a floor area of 26 sq meters that has wet underfloor heating (in liquid screed)... but the area to be tiled also incorporate the old non heated concrete floor of 9 sq meters so what to do ????? as some of the floor will expand and some wont.
I know I will have to use expansion strips but will I need a decoupling layer too which adhesive etc ?
Now Im no virgin to tiling floors and walls I mainy do bathroom to pay the bills which normal involves tiling in a shower or around a bath or even doing the floor