LS460 AWD, what is the interval to change this fluid? I can't find it in the user manual and can't seem to find answer, only to "inspect". I've done the rear-diff fluid change.

I would do 60k miles change interval. Make sure to use OEM or high quality aftermarket fluids.

What are you planning to use for your transfer case?

This is a very reasonable interval. 40k to 60k is the general “conventional wisdom,” 40k side for harder-use situations/vehicles and 60k for milder use vehicles. Should last forever with that. I use LubeGard gear oil supplement (2oz/qt) in my diffs now. Great success w/that in a 4x4 rear diff so now using it in all (it’s cheap enough to do so).

I went to a shop to have some fluids replaced, including rear diff. I did not mention front diff/transfer case. Is it normal and expected to have both done at same time? Paper work doesn’t mention front was completed. I didn’t know there was a front one! I can ask them tomorrow, but as a woman, I’m a little embarrassed by it.

Front differential gets neglected for some reason.

So the tcase uses regular gl5 gear oil?

Transfer case and differential oils requirements are in your owner's manual.