The design consists of one large PCB that acts as an interconnect for sub boards, the benefit is I can test different designs and easily leave parts out that I don't need.  For example for my phono stage I do not need a standby power rail, so I left that module out of the design.  

The power supply interconnect board accepts power from a simple DC source or from a USB PC negotiation module.  A P channel MOSFET is used to control power to the remainder of the board.  A module is used to invert the DC supply and both the original DC rail and inverted rails are fed into a module meant to clean the rail and final regulation.  The output from the MOSFET and the final symmetrical rails are provided to the output connector.

A final linear step is added more or less because its expected and does help to isolate noise from switching supplies.

Of the modules developed for this new power supply I made a mistake with the linear power supply.  I suspect at this point I simply left the spacing constraints to tight in PCB layout profile causing problems with the manufacturing of the PCB's.  After noticing the problem with the board I just bodged a simple fix to move the project along.

Objective 2, simple to create a functioning phono stage however I did want to make it modular assuming I would either make mistakes or want to fiddle with the decompression/amplification circuit.

I didn't need to design a phono stage myself as googling "RIAA phono stage circuit" results in many designs just posted to the internet.  I settled on a design that used opamps for the sake of simplicity and my recent experience using opamps to create headphone amps.  The current generation of high end "audiophile" opamps compete very well with discrete designs for a fraction of the cost.

https://sound-au.com/project06.htm

The only down side to my design that I've come across so far is a loud pop from the speakers, so I may add some sort of muting circuit to this.  In the meantime I simply power the phono stage on before I power on my amplifier.

Most of the case and other mechanical parts are 3D printed or I used a laser cutter to cut 2mm plywood to create the case and inner sctructure to hold the circuit boards.