a) The grass palette that you put in the 8th spot will only show up in the maps that you insert it in, since the 8th palette is a tileset 2 specific palette. This means you have to recreate the same palette every single map, in the 8th palette in order to avoid graphic problems. Time consuming, but not a huge problem.
b) Since you've used a palette for the pink roof, the body of the house, and the plants, that takes up three palettes. Since 7 and up (yes, I checked) are tileset 2 palettes, this means that you have 7-9 taken up. This leaves three more palettes (10-12) for you to use for anything in that map.
You should have room to create a new palette for the platforms. Also, I would work on combining as many palettes as possible into the first 6, it makes your life a lot easier. Just make sure you don't overwrite any animation colors.
You can export a pallet, and import one. I've been doing this for my pallet 8. I have the game mapped up to 6 gyms. And scripted up to gym one. It should be possible for me to make the platform something else. Thanks!