To answer number 2, Soundstorm should have everything you need (and it definitely has a LOT more than the SI 5000 series give you for variety on individual cars, if the car in question is even recorded/mastered decently) - but it depends on the vehicle source since some cars are more full recording sets than others. Source is everything with cutting vehicles (both the right kind of engine, and the right amount of record varieties). having the right source can make cutting vehicles pretty straightforward, but having the wrong source can be a nightmare and detriment.
I don't know what kind of car you're cutting for, so I can't point you to an appropriate starting point, but check out the Chrysler Sebring, Saab 900, Mercedes E320, Mercedes 220SE, Cadillac Escalade, Chevrolet C-30 Tow Truck, Ford Dually, Crown Vic. As I recall these are pretty complete sets (I'm sure there's other too but they don't immediately come to mind). For doing car bits like what you stated, the key is to use the onboard EXT mics for doing the car itself (usually they come split as engine block and tailpipe, and have chase driving, city driving, and maneuvers varieties - the Sebring set is a perfect example of this), and use the offboard EXT material as needed to "bridge" some maneuvers that need it (such as using an EXT washy BY to help blend between source material). And sometimes you need the stereo image of an offboard EXT accel by or aggressive maneuver to sell the motion of the car onscreen when it's close to camera and POVs are shifting. If you are working with only the offboard EXT, I agree, cutting said sequence will be pretty damn hard - but when you get the onboard EXT into the mix, it opens up a new world of cutting vehicles. Hope that helps!
Also, don't under-estimate the power of the Reverse tool. Oddly enough, engines can be reversed and they're quite forgiving in that respect. And as I heard Jay mention before on here somewhere, sometimes you have to mix car source to get the right sound (Case in point, one time I slightly pitched down the Sebring source for the INT scenes of an SUV, and on the EXT I used my Subaru Forster for a throatier, punchier sound since the Sebring would sound too small for the EXT).