Your requirements don’t seem so wild so my reckoning is that you might end up with something close enough to what you want, if you pick the most favourable combo of AZERTY and numpad units.
I’m here because the system notified me of the link to my post! As you point out there is not room to make something truly custom. As somebody acclimatised now to an Atreus with a non-querty layout, I scoff at the very modest requirements of the OP 
. I have been waiting two and a half years for a staggered column, or ortholinear design to emerge.
Although Framework tell us their machines can be customised, that customisability is - as I see it - generally kept within certain guard-rails determined by the design itself. The dearth of successful aftermarket keyboard projects suggests that true input customisation lies outside these guard-rails. That is why I thought an aftermarket chassis might help, it would break out of the straightjacket imposed by the present keyboard depth.