>why the separate contactor?  
Tracy,
Are you saying a contactor isnt needed for the starter?
John Slade

The starter solenoid is itself a large contactor.  At the same time it
closes the contacts for the motor current, it also engages the starter
drive gear.  I had concluded also that using a heavy "contactor" relay
in the starter circuit was redundant; but be aware that the starter
solenoid has a very large in-rush current, and a fairly high holding
current - just guessing maybe 7-10 amps.  I was just testing my starter
engagement a couple of days ago by touching the alligator clip on a
jumper lead to the battery terminal.  Lots of sparks making and
breaking, and the jumper (about a #20 wire) heated up pretty quickly on
the holding current.

If you use an intermediate relay, make it pretty heavy duty and use
spike suppression; or if not - likewise on your push button switch.

Al