Okay, I've decided that the final export resolution will be 2 pixels per metre. This will result in a map slightly smaller than 7500x7500 pixels (iirc). Hopefully this won't be considered too big.

@Korash
I've decided to go with a non-exaggerated scale (except for the walls maybe).

@Tigon
I was considering a technological level that would roughly be the equivalent of late 18th, early 19th century England based on magic instead of tech. The high level of detail is explained in the 'copyright info' on the map. Basically, it is a magically 'printed' map using information obtained from scrying. Now that I have more time to work on this I'm going to be trying out multiple looks in an attempt to find something that doesn't look so modern, yet still retains the same level of detail.
Actually, I forgot to include the Travel Arches. I'm trying to find a better way of depicting the working Arch as opposed to all the other Arches which fall into two categories (receiving and completely dead).