Rondidon,
You obviously have a great deal of time invested in both, your project and in understanding 3dgs...
I too have had issues with system crashes in the past. Therefore, I also watch these variables closly.

The optimizing process is a major concern constantly as I create a new project. You are right to use .dds textures wherever you can.
My biggest concern and problems in the past have been with to high a nexes value and I have found that the best way to keep that number as low as possable is to minimize the number of entities in a level.

As I understand, as the engine loads a level, it allocated memory for each entity by counting both wed placed objects and script placed objects.
That is why I created a run-time vegetation placement script that allows for trees etc to be placed when the player is close to the ground and removed as it's no longer required. That enables the forest/houses etc. count to be low at engine level load and therefore a lower nexes requirement.

With the A8.04.2b version a new convienient method of placing vegetation was included called, the "ent_seed" function and can be used to seed entities on terrain, depending on colors on a mask image. That may help you.

Other than memory allocated for texture and the level entity count value, there is the concern of verticie count value especially with the animated player. I do suggest in your optimizing process that you also constantly review the verticie count and minimize as you can...
Best of luck...