Hello!
I did this kind of optimization for my upcoming game.
It included reducing polygon count on assets, making LODs, making texture atlases to combine various assets into a single material to reduce batches, combine diffuse and normal to have a single texture, atlas particle sprites to reduce batches, tweaking assets settings to reduce memory in unity, among others.
I use the following tools to do the optimizations: Maya, Photoshop, Simplygon.
If you are interested to work with me, due to the extensive amount of work and time that is required to do all the optimizations I will only do it by the hour, with an hourly rate of 10$.
Best regards,
Vladimir.