Drivers that come from "fendered" cars seems to take to legends easier than those winged maniacs. I would imagine that your seat time in modifieds will serve you well. You will have to learn what the car likes initially, but you should easily get a feel for how it needs to be run.
As far as how the car will react to dirt, I can only suggest that you "keep it up on the bars". Modified and late model guys know what I'm talking about. If you stay out of the gas too much in the corners, legends have a tendency to get tight. You will want to keep the rear broke free while balancing to keep fwd bite. As far as entry, you may or may not have to throw it into the corner. It all depends on your base setup. I personally, do not throw the car on entry. I use a combination of braking and mashing the throttle.
Running the top on a track with a curb is not impossible, it just requires some smarts. Generally, when running the top, I try to keep the car straighter (more like an asphalt line) and using the curb is able to be done, but remember that the right rear bumper will "catch" the berm if you hang it out too much. An occasional bounce off the berm is okay, but a slider to parking the right rear on the curb will bend the panhard bar easily. Also, jumping, and getting above the cushion into the marbles increases the chance of knocking oil lines off the oil coolers or mudding up the steering rack.
As far as adjustments that the others mentioned, I can't say I agree or disagree. Yes, in theory the track that goes dry would generally need a tighter car for feature time, but.... If the track lays rubber, you may need to loosen the car for the feature. We have run heavy tracks in the heat race and by feature they took rubber. The American racers sometimes react better to rubber down by freeing up the car.
Ultimately, rely on the knowledge you have with mods. The feel you get from the car will tell you what you need from race to race. As far as your confusion about the rf spring adjustment, I think you must be used to running a solid front axle??? With independent corner suspension (double a-arm), a softer rf spring will loosen the car on entry. I would recommend having your ride heights anywhere between 4 1/4" to 5"+. High ride heights will let the car roll and transfer weight easier (and keep the right side frame rail from bouncing off the track).
Don't be afraid to make adjustments. Sorry 90Legend, but a 1/4 to 1/2 turn isn't an adjustment, it just makes you feel better. By the threads on the adjuster, a full turn is only 1/16" in ride height. A 1/16" inch moves your cross weight maybe 0.2%. When I make adjustments, its at least 2 or 3 full turns and makes at least 1% difference in cross weight.
Your first day is gonna be more about feeling out the car than worrying about adjustments. Be smart, have fun, and earn a ride for next year by bringing it home in one piece. Speed will come with more seat time.