Hi,
Thanks for posting and welcome to the Fusion 360 community forum!
There are controls for Grid display in the Grid and Snaps menu, on the Navigation tool bar.

However, the grid display is also partially determined by object size. So you may need to create an object large enough to push the grid boundary farther out for your situation. A sketch with a construction circle is a good way to do this. Once you have a 3D model doing the same job, just turn off the sketch or delete it.

The answer to your second question is to turn off Ground Plane in the Effects menu.

I hope this helps. Please let us know if you have more questions.
Thanks,
Phil Eichmiller
Software Engineer
Quality Assurance
Autodesk, Inc.