Wouldn't you mind sharing your plan for disrupting the city here?

It depends on the difficulty, resources, and many other factors. It's better to upgrade Gremlins quickly because the difference between the regular ones and the upgraded ones is very significant in terms of initiative. Regular ones have 7, while the upgraded ones have 11 and 12, and it's rare for any other units to have such a high initiative. Gargoyles can also be built right away; they often serve as a shield, and a couple of Mage Guilds can be added, and then, as you develop, you can build the next schools. If you already have the basics of some magic, then it's worth building the third level right away. Next, build Golems, which can be sent into battle, and at the end of the battle, the Gremlins will repair them. But first, I always build buildings that generate income because that's usually where the biggest problems are at the beginning. I also usually try to build a Warehouse quickly, but it's expensive, so you need to consider the cost and choose the best time. You also need to build the Djinn building as soon as possible because it unlocks the Treasury, which brings in extra gold each day.
And if you're developing through Chaos magic, it's better to build Obsidian Golems sooner. This way, you can simultaneously attack enemies with some mass magic and heal the Golems.
Well, that's how I usually do it, but, as I said, I'm not a big fan of this race, and I haven't played as it as much as I have with most other races. Maybe if there are any experts on this race on the forum, they can advise you on a different approach.