yea with me audio comes first, ill look into the nexus, only real req for phone for best function is camera on the corner edge so when you flip screen up camera is visible, keeping all guts in the phone it-self makes this much easier
battery space in phone can fit various things like usb hub chip so keyboard is working and hopefully charging also so no external charger is needed like my old fast charger for the dual battery cover for the N900, also fit space for 2x3W amp for speakers, this can be made by shorting the jack detect with a switch that also poweres on the amp, then normal operation will be internal speaker of android phone being used, when better audio is needed you activate the amp and jack detect, audio from jack plug also goes into the amp, will see if any filtering/resistors is needed when i get to it to avoid any noise.
Speaker function (calls) is another thing...

The 3D printed Speakers i made are also VERY good, did also use a lot of time and $ to develop them