Hi Ian
For some reason , I find your first mechanical choice very good, euro rack is professional, industry standard for decade and truly modular, way more than 500 series..., it will be difficult to beat this, especially if your not so good with mechanic.
I personally won't take the 500 series example for control density, over populated knob in this format is just a pain to work with
Maybe have a look at all Fischer sub rack options. IIRC you use the full extruded enclosure, A series. Have a look at F or I series, with shielded side panel made of bended alu,
For example, F series enclosure give you 14(hp)*5.08-16= 55mm, where A series (the one you use) give you 42mm (14*5.08-29.4)
The I series is even better for room, 65 usable mm for 14hp, and 29.5mm for your 7hp (new

) design.
Combination of I series and small cut at shield panel and/or PCB at front panel side allow you to place control close to edge !
Best
Zam