I have gutted my entire bathroom. I am planning on installing regular drywall except near the tub/shower where I will use backer board. Is this OK? I thought since the walls behind the vanity and toilet will not have much if any direct contact with water it shouldn't be a problem. I am also planning on tiling over the drywall. Also, I am installing insulation in the walls except on the tub wall since it is facing into the house. Do I need to use a moister barrier between the insulation and the drywall?

They make waterproof sheetrock for high moisture applications.

You're probably going to want to use cement board. Especially for tiled walls and ceiling where you need some extra strength.

They also make some stuff called greenboard. Greenboard is moisture repellent with different paper and bonding agent but isn't really as strong. I'd stick to the cement board.

You'll also want to caulk every nook & cranny and add a sealing/primer coat or two before you tile & paint.

When painting/priming, check out this stuff called Kilz. Masterchem Industries, Inc.

Have fun & good luck.

Insulation comes either faced or unfaced. You want the faced insulation, that is your moisture barrier. The moisture barrier always goes to the warm side. Adding an additional moisture barrier would not be recommended.

Using regular drywall in the non-shower ares is fine but personally I like to use green board through out the bathroom. The extra resistance to moisture in an high humidity area is well worth the extra cost in my opinion.