you can't miss the preferred parking at Fiesta. . you pass it 1st, before you get to the General parking. (there will be someone at the entrance cones to the preferred area).
as to your Flash Pass - personally, I would not waste them on Superman (it's a people eater. . . even if a long line, it moves fast), or Roadrunner (which can get long lines if the park is crowded, but at the end of the day it's an Arrow Mine train. a good one, but still).
I'd use those 2 "saved" skip the lines for Wonder Woman (capacity is awful, and the ride is incredible), and Joker (due to the queue, they often run non-full cycles, as it takes them a long time to get folks thru the fun-house - which is AWESOME by the way, and the Flash Pass gets you in line just in front of the funhouse instead of the long snaking queue.
it's your 1st time at the park so will mention: Poltergeist Flash Pass will put you directly in the Station (it's the best skip the line in the park), Iron Rattler puts you one ramp down from the station - but they have been holding the general line before that point, so it's basically a station wait. The issue you'll have is if the park IS crowded? the Iron Rattler flash pass entrance is a decent way inside the main queue - so if busy, and the line spills out of the queue? you'll have to get past people to get to the Flash Pass entrance. (same thing with Wonder Woman - flash pass entrance is way down in the queue, so you'll have to "excuse me" past a lot of folks to get to that entrance. . . but people are polite at SFFT and will move over to let you pass).
rides unique to SFFT not to miss:
Hustler (it's teacups themed to pool balls.. fantastic)
Daredevil Dive (newest ride, so might have a wait)
the boardwalk spinner rides: Spinsanity (next gen Tilt-a-whirl) & Wave Runner (Huss Scrambler that runs a great program)
Pirates of the Deep Sea (also on Boardwalk, behind wave runner) - an inhouse created dark shooting ride. Impressive as all hell for a Six Flags park.
Bug's Whitewater Rapids. (a wonderfully themed flume ride in the Spassburg section. It's been down for refurb on my last visit in late Feb, but I think is supposed to be back up?)