Since you re Building a new home seek expert consultation regarding the listening room, this is of paramount value for you.
In particular, you might reconsider the 5m x 5m dimension. A square room generally invites the most standing waves. Find some odd dimensions or get all Golden Ratio for example.
It would also be worth your time (and fun!) to spend a weekend at an audio show. Unless you are in a major city with good brick-and-mortar options, this is the only way to hear a lot of things and find a frame of reference for the kinds of gear you like and don't. Unless you're spending a half-million dollars, your system will involve compromise; hearing a number of rigs is the only way to understand which compromises you are happiest to live with.