As regards width : it seems to be recommended that 4’ x 2’6’’ is preferable, rather than 4x2’ for a ‘roundy roundy’ to allow for curve radius (a little bit more than the recommended minimum) otherwise you may struggle depending on choice of prototype.
Kato Track- yukk! Similar qualities to Hornby Dublo tinplate...( just my opinion) - it looks horrible!! Peco code 55 , if nicely ballasted and weathered looks much nicer, and that is before you look at alternatives such as ‘Finetrax’
Setrack is horrible, even though’ Unitracck’ is easy to assemble (that is about the only thing going for it!).