Keep in mind that once you have a 'odd' size tank, getting equipment to fit may become difficult. Things like the glass canopy will also have to be custom. If you use a HOB filter, will it fit or will it reach down so low that the intake won't allow it to rest on the back of the tank? None of this is insurmountable, but it IS something to consider. If instead you use a submersible filter, that too may be too high to fit, if you want the proper size for the tank volume.
If you can work around the maneuvering for access to clean etc., (with the cupboard above), would something like submersible LED lighting help with clearance? Don't know if you have it there, but the Marineland Hidden LED light strip I have on one of my tanks is completely submersible. I think with what you are contemplating, you need to have ALL the parts in mind before you start with a custom build. Just my opinion, with some ideas tossed in.
If you can work around the maneuvering for access to clean etc., (with the cupboard above), would something like submersible LED lighting help with clearance? Don't know if you have it there, but the Marineland Hidden LED light strip I have on one of my tanks is completely submersible. I think with what you are contemplating, you need to have ALL the parts in mind before you start with a custom build. Just my opinion, with some ideas tossed in.