Before you order the case ...
Considering that your buffalo build will have AT LEAST 2 trafos, Placid HD, Placid BP, Buffalo Board, Legato, Amanero... I Wonder if the monolith (PSU + PSU Board + Amp Board) will fit... seems big...
Also:
Considering that you may go dual mono
Considering that you also ordered OPC wire SE-SE, BAL-BAL and 3 PSU
Considering that you will want a NTD1 v2 when I got mine that could ruin your legato stackability.
Considering that you may upgrade buffalo PSU (let's say Salas SSLV instead of placid, OPC shunt instead of trident)
You won't fit il all !!!
You could optimize trafos with a custom big one that will handle everything (from audi*ph*nics)
You should plan it seriously with some paper canva at real size. And consider a big box for your dac alone until you reach the end of DIY upgraditis
PS: I'm well informed about what Ony is planning