Get rid of the cable and car arrangement ASAP. I have heard stories where fingers were crushed and/or severed by being caught up in the car.
A fixed main is also terrible. With no diamonds and a super stiff mast the boat is very hard to depower. You'll need the traveler. It's a pig without a jib so the traveler is all you've got.
Words of wisdom on a SC17: Weight FORWARD. Add 18" to your tiller extension. You'll find your can point crazy high if you're up on the front beam or even in front of the beam. In a puff, step forward even further. And wear goggles as it's the wettest lee bow you'll ever see. Wahoo! What a hoot!
Sail it solo.