I planned to use Peco code 55 track from the outset. This looks nice, has electrofrog points and has the "scissors crossover" available.
I wanted to avoid curves that looked daft, while space constraints did not permit prototypical radii. Most rolling stock is specified to operate down to 9" radius; I tested several trains and they negotiated it with ease. (I do know that some co-co type diesel locos will NOT run reliably around 8.5" radius bends). My plan was to keep radii to 12" minimum if possible, and use larger radii on visible sections.
The Peco 26.5mm track spacing leads to collisions on tight corners, and that spacing can only be used on 15" and above radius. Realistically, to allow margin for error, the minimum radius used for that spacing should probably be 18". At smaller radii, the gap needs to be opened out by 3-4mm.
In practice I have tried to avoid 12" radii except in hidden areas, and most curves are nearer 18" radius. All visible pointwork will be medium radius (18").