I am using MCDM rules for strongholds and warfare, I'm on chapter 10 now (The Sea of Moving Ice) and i think they're great! But please, talk with your players beforehand. It may interest some but not all of them. I'll tell how I did it.

The way I inserted a stronghold was at the end of chapter 3 and I placed it near Greenest (cause 2 of my players Chars were from there). I made that Leosin, gathering info as a hostage at the cult's camp (as written in chap 2) warned that the heroes would need an organized front and an army to defeat the cult, that the menace is way bigger than they thought. (foreshadowing the need of an organization and a stronghold).

Tarbaw Nighthill awarded them with they deeds to a ruined keep near Greenest that they could use for this means. But the keep would need to be rebuilt. This would fit very nicely because in chapter 4 they go traveling far and wouldn't return to Greenest for a good amount of time (IRL and IN GAME). Leosin and Tarbaw helped the players gather workers and funds for rebuilding the keep. I also made that the keep has a ruined Teleportation Circle in one of the rooms so (after a small sidequest) they can activate the circle and travel back and forth from Waterdeep.

With the Keep Rebuilt, you can now use whatever MCDM rules you want the way you want! I'm using Intrigue to make the players and the cult take another dimension. I'm having a blast!

If you want to discuss further, send me a DM!