First, congrats on your maiden flight success!
Dual rates = switch activated throw limits. Its OK to use both D/R and Expo at once.... as long as you understand what they are both doing and how it is setup.
Most experienced flyers will put extra expo in on high rates to give the plane a similar feel around center stick position regardless of dual rate setting.
Richard Lindberg covers it nicely here:
http://www.rmfm.org/dual_rates_and_exponential1.htm
Some used to call dual rate switches "Crash switches", and here's why:
Dual Rates are basically like moving the clevis on the elevator (rudder, aileron) while in flight! So if you think you are in low rates but are actually in high during landing or takeoff, you will overcontrol and probably crash. I once put a P.O.S. plane in because I thought I was in high rates, pulled from inverted for a half loop that should've ended up 15 feet off the ground..... but it didn't loop tight enough because I was on low rates. Yes, I was hotdogging and therefore got what I deserved, but I didn't really deserve it- the low half loop was a move I had done before.

For an example of dual rates usage, these days (15 yrs of flying) I usually set the dual rates to the standard "kit" throws on low switch position, then put the high switches 20% higher than that for starters. That way, if I need or want more throw, I kick it up to high rates. This would make a 1" elevator throw on low rates go to 1.2 inches on high rates.
A flick of the switch and I can go from tame to squirrely or the other way, depending on whether I am feeling nervous, or daring.
Also, as the plane slows down for landing (and other less dangerous low speed stunts like harriers!) you sometimes need the extra throw of high rates, say on ailerons for a cross-windy day.

Another way to use dual rates is the "other" way, which I did up until about the 3 yr mark: set high rates for the recommended kit throws and low rates at 80% of that in case you get the mid-flight jitters and want to settle down. Low rates tend to keep your knees from shaking so much.... but you may run out of control authority (not enough throw) during low speed manouvers if you are on low rates.

Expo, on the other hand, can be used on either or both positions of the dual rates switch (or neither). It basically softens up the middle of your stick response but goes to the same throw at full stick. This means that 10 degrees of stick motion near center may only give you 5 degrees at the elevator, but the same 10 degrees of stick motion at the extreme of stick travel may give you 15 degrees at the surface. So, by making up travel in the last few degrees of stick throw the total throw never changes with expo, on the other hand, dual rates actually change the total throw.
Be sure and use NEGATIVE expo numbers for a Futaba and Airtronics radios or you get the opposite undesired effect and the plane is nearly impossible to fly- jumps all over the place on the slightest bump of the stick.

Based on your maiden flight post, I'd suggest staying with what you're used to (no dual rates) and then dial in dual rates later, when you want more throw for 3D but want to be able to revert to the plane you had gotten used to with the flick of a switch(or two**). Right now, you may find learning and remembering when to throw the switches too much at once while you are getting used to a fairly responsive stunt plane like the Extra. Read your manual carefully when first using both expo and dual rates and check the surfaces with a ruler and using the graduation marks on the base of the stick pots to confirm that you are getting the desired effect at the control surface before trying it out in the air. Your maiden flight description is consistent with inverted expo settings, or just jitters, or just stunt plane vs trainer. Be sure and confirm the sign on your expo settings if this is your first venture into expo. But I'd guess at 40% expo, if you got her in OK, you have them the right way.

Wheels Down!
Dave

**Dual rates are usually on different switches for elevator and aileron. Sometimes you only want one to change its sensitivity, and not the other.