Hi jadedofmara,
Instacrashes can definitely be a headache, here are a couple of things you can try to get a map running again - these don't always work, but I find them often helpful in developing a custom map.
1: Check the "player-prev" text file in the parent folder to the "mod" folder. Somewhere in the file will be a line starting CityDefinition.FromUGC: Loading (your map name) from JSON.. Under this line will be errors that the game picked up during launch. I find this most useful when the game launches successfully but says "error in loading (map name)", or words to that effect.
2: Remove your new map from the mod folder and start with a clean map file you know works. Copy and paste information to replace part by part, testing a launch each time, and creating backups of successes. This takes a little longer, but can help if you really can't find the source of an error.
3: Check spellings and ID links between files - this may be the issue if the mod guide code isn't working. It could also be a missing or unnecessary comma.
Hope this helps - error fixing for custom maps can be a pain to resolve!