I don't think that will work.
If you dont use both P0, P2 and a latch, you will have holes 256 bytes wide in your mem.mapped devices.
Not if he uses internal RAM only, switching to external 'RAM' his devices would be addressed by xxaa (x = don't care, aa = address)
I wouldn't load the micro/xtal with anything exept the usual caps. If you need the clock for anything else, either use a portpin and do it in software, or use a oscillator chip. I thing you can get them with several outputs and a (programable?) divider. Check EPSON or SEIKO, but they might be rather expensive.
I would, but only if I had the right to kill thr PCB lsyout person. If the clock buffer is a schmitt trigger and is less than a 1/4"/5mm trace from the XTAL2 and the capacitor is reduced by the value of the gates input capacitance it works quite well. Again only do it if you can enforce a short trace.

Ha' en god weekend, du ogsaa!

Erik