Hi Quenten!

Number of gates

This option was introduced when I didn't have convenient UI tools - that's the main reason why this parameter is only possible to specify as a URL variable. Since then I've created a decent UI library, so most likely there will be a way to request a desired number of gates/roads right in the generator. There is still that issue of not being able to create more roads than a specific maximum value which is not known until the city is actually generated. This may look confusing.

Custom size

There are two problems with very large cities:

1. They are very slow to generate. That's probably not a huge problem especially if I'll be able to implement generation in background to keep the web page responsive. Still, I'm not comfortable with the idea that generation can take more than a couple of second. Btw, how long did it take generate this city of yours?
2. Very large cities look wrong. Not as wrong as they used to look but still wrong. So while MFCG can probably generate a city of size 500, I don't want to advertise this fact by exposing a button "Size=500". But those who needs cities this big still can try to get them. I'll probably add "Very large" later for cities of 50-75 (or so) wards.

P.S. Nice maps!