Technically, all rallycross courses need to be safe for street vehicles.
Practically, the worst thing you will have to worry about will be debeading, so crank your front tires up to max pressure. Really, debeading is only due to doing something dumb like plowing into a rut with the steering turned and it's fairly rare. Subaru chassis are very robust and the only time I've seen breakage was when someone found out the fun way that one of his lower control arm bolts was missing. (Threads in shell were stripped from a previous repair) Oh, and the time someone was at the top of 2nd gear and caught 1st instead of 3rd. Susprisingly, it was a drive axle that gave way.
I am sure you will hear this a bazillion times, but it is key to not worry about your times and just have fun. 99.999% of people don't do well at all at their first rallycross. With that in mind, focusing on having fun instead of trying to be competitive will ensure that you'll have a good time, and you'll go to more events (jooooiiiin uusssss....) and with experience you'll get speed.
Yes, technically, your car is PA. Most regions are soft on noobs and if you went and spoke with the other Stock class people, they may let you run Stock. Class really does not matter in rallycross, though. It's not uncommon for first overall to be a "lower class" car with a good driver.