You guys are thinking in terms of other games. In FE we will be making stamps, not maps. We will make tons of stamps that are patched together to make the whole map. Sure you might make a copy of some map from MoM if you really wanted to pay homage, but the most fun will be had by adding more unique stamps. The thing we need the devs to do is make sure the starting postion stamps are fair and equal. And to make sure that resources and monsters are also equal.
If I understand correctly, the game (when set on randomize), in a 90X90 map, will take say 100 pieces of pre-made pieces, each of 9X9 tiles, and puzzle them together to form the map. Modders and devs can easily create a new piece (or stamp), and the game will automatically place it into the maps.
Assuming this is the case, a modding tool should be added for these stamps, with, by definition, this field: starting location value, starting location range minimum, starting location range & chance.
The value, placed between 0-100 will decide a chance for that specific piece to be the starting location. I assume you can manually set the specifics, such as making sure the middle tile has a 3/3/2 or other size. With each randomize, the game will have higher chances to roll the lower chances. Note that a 99 stamp will occur 33 times more than a 3 stamp.
Range minimum will decide the minimum range (in stamps) from the starting location. A range minimum of 3 will means there are 2 stamps between this stamp and a starting location, and if map too small it will never appear.
Range & chance similar to range minimum, but allows to reduce the chances that the tile will be close, instead of preventing it (minimum is chance=0)