Firstly, GP thats a great map - your usual excellent standard.

For the file size I think that there is a general 5K limit or so which is some kind of bug in the forum. This one is 3K or so and less than this limit.

For file byte size then you can save images as reduced quality in JPG to reduce the file size. There was a lot of banter about all of this in the May 08 challenge which had an upper file size limit as part of the challenge. Threads for tips about reducing file size were posted as part of that. Notably...

http://www.cartographersguild.com/showthread.php?t=1956