If we take Stationary Lights as an example, the engine itself will not allow you to have more than 4 sources in one place…
For Movable - you’ll know when it’s too much - when your FPS drops below 30… 
If everything is baked, then the cost of light at runtime will be zero (almost).
Therefore, all sources must initially be Static and baked.
If light can hit a moving object (you need moving shadows), then it must be Stationary.
If the source itself must move, then it can only be Movable.
Disabling this feature is the surest solution to improve performance. 
- Bake all the lighting you can.
- For dynamic lights - reduce the radius of action (save the engine from unnecessary calculations).
- Turn off shadows on objects that have little effect on the image (but also consume resources).
- (?) Come up with a way to “trick” the player by creating the illusion of a picture, rather than creating one directly.