Sorry you're running into so much trouble. The editor's relatively flexible, but there's a lot to learn at first.
The trouble with your tile warp lies with the Type. The Cave/Item Cellar type is meant for warping to a sort of "sub room" to the screen you're on. Think of the caves in the original Legend of Zelda where you get items and rupees and such. It warps you to a specific screen that's the same for the whole map. If you haven't checked out the ZCWiki yet, I highly recommend it. It's a great reference, and will probably answer a lot of questions for you with a quick search. Here's its explanation of warps, with a list of what the different types do. In this case, you could possibly use the Entrance/Exit type, or one of the instant warp with transitions.
For b, the confusing thing here is that changing the palette on the screens themselves is just a preview. Actually changing the palette needs to be done through the DMap editor. Quest->DMaps, then the Appearance tab. There'll be a place to select the palette there.