Do you have any suggestions on rocker switch locations that you posted? That is the switch I used on my 2005 DL 1000 Vstrom. It had plenty of room to mount switches.
Always fun to plan these things. I know that your current plan is to mount your switches in a single location. You might consider having your auxiliary lights switch on the handlebar so that you can flip them on / off with your left thumb. Modern aux lights are pretty bright for oncoming traffic. The switch I use is nestled in between the switch box and mirror stanchion. It has a activation light and is made of aluminum. (Amazon)
As for the dash realestate, there are two flat spots on the lower face of each side. There is not a lot of depth behind them but they are a good spot to mount a "project box". There are a ton of size choices, as you know. I use the black nylon ones for switches, etc. I mount them with the "back side" facing out for easy access, later. Don't know if you have already picked out your heated grips. I chose the Oxford not just because they are good but the control box is just right to velcro to that area on the left side of the dash.
Lastly, for my heated gear, I have mounted the switching into the plastic body panel that runs along the side of the bike below the seat. Again on the left side. I find it to be very natural to reach while I'm riding. And because I run that gear directly from the battery, it is a very short run of wire.
Not the same as your plan but hope it helps.
Current Rides: '14 DL1000 ADV, '06 SV650N, '93 900CBRR, '74 Ducati 750GT ['02 BMW K1200rs SOLD Aug '17]