Large Mesh Colliders and character collider not coliding

Hello all,

Thanks for any help you could through my way. I am just starting a game and i would like to have a huge play space. i have created a modeled plane in blender for my terrain and exported it as fbx. I imported it to my project and applied a mesh collider in the import settings at re-dragged it to my scene view. i then added a pre-made character from the asset store with a mesh collider to the scene.

I clicked play after adding a controller scrip and expecting everything to go wrong. blah, my toon falls through the map slowly. i am able to move in all direction but the terrain plane i modeled is acting like its not there. i can see it rendered but i pass through it like nothing. i have a rigidbody on the toon that i am using to move with my controller script.

i have tried other colliders but it results with my character being thrown to a high level in the sky and walking on a flat invisible area. Let me know what is needed to diagnose or add incite to this i will continue tinkering