Hi Nick,
The ‘oldschool’ way of doing this is to have a collision mesh prefixed with 'UCX_ ’ in your modeling tools
But now I think we could get good results with the in-editor modeling tools. (When in Modeling mode go to ‘Attribs’ section to see collision editing toolset)
About the wireframe worldsphere - are you talking in the context of the Static Mesh Viewer? If so: go to Window → Preview Scene Settings, and turn off ‘Show Environment’
Let us know how it goes!