Using split surfaces when modeling contact?

Yes it is helpful if only because you can control the mesh in those areas. And there is no point in placing contact elements on parts of a surface that have no chance of making contact.

yes that will theoretically speed up contact solutions since there are fewer surfaces on which to iterate and search for changing contact conditions. You might try it with "Low order" (or "Draft Quality") elements (initially, anyway) to get a faster turn-around in solution time and determine if the contact surfaces are behaving as expected (you could more quickly observe surface separations if they are happening- oscillations in contact surfaces 'bouncing' tends to increase solution times).