You can rent a helmet from OG Racing for about $35/weekend (and they'll mail it to you). You then get $35 off if you buy a helmet from them (but if you rent more than once, you still only get the first rental back as discount).
There is a good possibility that your suspension bushings (torsion bar bushings) are worn if they're original. Just about all of us tracked our cars before we refreshed the bushings, and I'm not aware anyone had a problem, but you might want someone to look at them (easy to tell on the rear - the cap on the swing arm will not be centered, with the weight of the car making the top smaller than the bottom).
The tech form mentions a fire extinguisher and roll bar - you don't need those, but if you have them the tech form has a place to mention it. Don't worry about either at this point.
x whatever on doing both the HPDC and the autocross route. You might try karting at Allsports GP (in Sterling
www.allsportsgp.com) over the winter. Great way to build car control skills and it's fun, too.