Using so many stageboxes and a dedicated monitor mixer reflects a lot of traditional thinking. That's how it used to be in the analog days, indeed. ;-) What you should do now is NOT thinking in connections to/from, but "thinking network". You have 32 inputs, 16 flex mixes and Main L/R. Any mixer and stagebox can feed inputs to the network and receive inputs from the network.
A SL 32 used as monitor mixer (in Monitor Mixer Mode) can feed all inputs to the network. It can, but it doesn't need any additional stagebox, unless you need some inputs (and outputs) at the other side of the stage. Save that money. Less material will anyway makes things easier.
Monitor Mixer Mode means that the SL 32 on stage will feed its own 16 outputs for flex mixes (aux, matrix), but receive Main L/R from FOH. The main mix level is simply not used. Just the Main L/R outputs are "lent" to the FOH console. You can also assign Main L/R to a stagebox as (additional) output.
The third option is to use the monitor mixer in Stand-Alone Mode, which means that it sources its inputs from the network, but cares for its own Main L/R and flex mixes. In this case you would need a stagebox to receive Main L/R from FOH, or an anlog XLR connection.
In both cases (Monitor Mixer or Stand-Alone Mode) all 16 flex mixes at FOH are independently available. This is a nice feature to feed live streams, delay lines, additonal rooms, recordings and for whatever a special mix is needed.
AVB streams 34 to 40 are reserved for the communication between the mixers. Whatever is sent to Aux In 1, Aux In 2 and Tape In (Digital Return) of the FOH console, it will automatically be routed to the monitor mixer and therefore be available in all aux mixes on stage. It is also possible to route FOH Main L/R to Aux In 1, Aux In 2 or Digital Return of the Stand Alone mixer and send the mix via linked auxes to the PA.
