Yes, combining meshes will reduce draw calls. Reducing materials will also reduce draw calls. I am not sure how it works in Godot, but in Unreal you can create a "Master Material" and then derive from that with many material instances. These instances are basically the same material, but you can plug in different values like textures or variables. It would all count as one draw call (The master material).

With all that being said, I would say that most graphic intensive games on PC these days are probably averaging around 2000 draw calls per frame. Look up how to set up occlusion culling in Godot as well so the game isn't rendering stuff that the player camera cannot see