Are you sure the paddocks are only 5000 sq ft? Out of my experience people usually under or over estimate size. For example, a regular 20 meter by 40 meter dressage ring is about 8712 sq ft.

To answer your question, harrowing or even mulching ( sort of) with a regular lawn mower works for me too. Its all about breaking up the poo in small enough pieces so they can be resolved back in the ground easily.