Even though I suggested 300 dpi for the map resolution. It really depends on how small your smallest text and or lineart objects are, as you could get away with and quite successfully staying at 200 dpi or even 150 dpi. It really depends on your map and what's on it.

Another thing mentioned earlier in this thread. Once you've got your layers placed on the map - flatten the image or export portions of your map as individual PNG/JPG/TIF files then composite the whole thing.

A flattened, layered map should be significantly smaller than 200 MB.

I deal with lots of maps at 300 dpi/24 x 36 that is less than 100 MB - it depends on how you save it, flatten, etc. Seriously consider a compressed JPG file as your final map for lowest, but still high quality, resolution.

GP