Yup I would be afraid to turn much of anything on especially if you are sailing off the hook or live on a mooring.
90ah to 50% depth of discharge (max draw down) = 45 usable amp hours. If on the hook or charging using only an alternator figure you'll only ever get back to roughly 80% of that 90ah capacity. So you now have only 72 ah's total available leaving you only 22 usable ah's before you hit a 50% depth of discharge.
A 22 ah bank is barely enough to be safe if you needed your running lights. Of course you can always go below 50% DOD but you'll be shortenting the battery life..
Yup! For now I pretty much only use the running lights (also LED - Aqua Signal Series 32) when the evening race runs long. I have yet to actually use the anchor light to anchor or use the mast head nav lights.
I also have a 90 AHr starter battery and a 1-all-2 switch. These batteries are from Walmart. They came with the boat. In the Spring I plan to replace them with actual quality batteries and add a 110VAC chargeing system. But, I do much more racing than cruising, so the batteries will be as small and light as I can safely get away with. Plus, the battery compartment is pretty small.
But as you said, for now, I turn on only what I need - VHF, GPS, instruments and when needed nav lights.