Thank you both for your responses. I wanted to post an update in case anyone else ever has a similar experience.
I tried taking my car out for a quick spin to see if it would make a difference, and sure enough, within a mile down the road the "No Start" indicator blinked off. Apparently, I did not add enough DEF to the tank the first time in order to remove the indicator. What big sigh of relief!
There are many posts regarding refilling the DEF, so I wanted to summarize a few things here for future readers:
There are two reservoirs that hold the DEF that are accessible by pushing firmly on the small triangle on the round disk on the driver's side of the rear bumper. I don't know the size, but I use a large Allen socket to twist off the caps on the reservoirs by hand and then only re-tighten the caps by hand.
The upper reservoir is the passive, higher capacity tank that holds 4.5 gallons. The bottom reservoir is the active, lower capacity tank that holds 1.6 gallons.
When refilling the tanks, be very patient and pour the DEF very slowly while allowing air to escape through the small diameter filler neck as you pour. Personally, I found it easier to use a funnel with a small hose on the end for the refilling. It is much easier to do with one person pouring and having a second person holding the funnel.
To make the refilling process easier, many have recommended purchasing a small 1/2 liter bottle intended to be used for emergency refills of the active reservoir and reusing the bottle as a funnel after its initial use. The next time I do a refill, I intend on cutting a hole on the bottom of the 1/2 liter bottle, screwing the bottle onto the filler neck, and pouring DEF from a larger (and cheaper) of DEF. As far as I know, pretty much all DEF is the same and there's no need to buy anything BMW branded. You do want to make sure that the fluid you are using is not over 2 years old, however, as it can degrade over time.
You also want to be careful when adding DEF not to overfill the tanks. Overfilling the upper, passive reservoir can cause the DEF to crystallize and therefore plug a vent on the tank. The crusted DEF is still soluble in the liquid DEF, however, so if it is crystallized you can soak the crusted area with DEF to clear it up.
Well, that's about all I know about it. I'm not a mechanic, so I fully admit that I may be missing something. I just wanted a central source where people can find this information quickly and hopefully save themselves from spending hundreds of dollars at the stealership when it can be taken of at home very easily.