I contacted a Buddy on FB who goes Topless...
He said your plan sounds pretty good but to go a little closer with rods around the riser... He uses 1/2" cold rolled steel cut 6" long (Does not like rebar) and goes about 2 1/2 to 2 3/4" spacing between rods... I think he uses strapping also not rope...
My personal opinion... For a 1 1/2" wide form using rope... I would go 1/2" rebar, 5" long, 2 1/2" spacing and 2" spacing near riser...