Increasing performance

I’m creating simulation for 4D chair. Done a lot, but performance getting worse in progress.
Map is huge, with many objects. I imagine good way to increasing performance - disabling distance objects, or models while they are not seen (behind hill). Now every object is loaded even if I don;t see them. Is there any way to do this with codding or other way ?
Second issue I’m having is shadow blinking, I read about it in many places, but no one has solution?
Third, water, if i enable water in my map, in specific, daytime water game has at least 8fps decrease.

for large scale maps a technique of two cameras are used in order to help performance, one camera set to only view the land hills cliffs basically the large objects with low texture quality/mipmap, and the other camera is set with a clipping distance close to the player and this shows small rocks grass and all the little things that you cant really see in the distance, also displays a higher quality in textures.

ive never made a large map before as i havent got the time at the moment, but if you play games like fallout you can notice this is what they have done. maybe someone can give a better description on how to properly do this, i cant remember the website i read about this.

  1. Try to use LOD (Level of Detail), which requires a pro version but can help improve greatly the performance. For very far object, they can be replaced by simple billboards.
  2. Make your objects static.
  3. Share materials as much as possible amongst your objects (all objects with greatest LOD can even use the same atlased texture).

Ok, I wasn’t expecting so much help, Thank you.
i tried texture baking, on terrain, it bakes it in very wrong way, shadows are not in exact place wherte they should be in baked mode. As example, track shadows appears, 5 meters from the track itself on terrain.
Texture atlas, (combining textures) I have done this all for my all models, example, this carriage uses only one texture:

Also, I tried playing with bias as well for texture blinking, it helps but just partly, it still blinks but just not that sharp.