Regarding dating serial numbers, when I ordered by NX5510 I had to wait to get one from the factory. Seems as though the 5510 is kind of a tweener, which means that they are unlikely to be sitting around on a lot (my dealer only had an NX4510 when I went there- it being a cab helped convince me to go with a cab). I seem to recall paying something like $36,500 or so, total. All is in the ballpark: as noted, a lot of machine for the money.
Stereos are quick installs. Just pick up a $5 wire harness (I'd have to look to see what it was I got- still not installed because I have yet to purchase a stereo- trying to lay low after spending for hydraulic top link and stuff for 3rd function, and my cameras and monitor [which were cheap]

). Most folks seem to not have to use a rear support (which would require popping off the cab top). But, yeah, I'll be getting a bluetooth unit as well (so I can keep in communication with at least the wife; always a good idea to have something to communicate with if you run into an emergency and are a ways away from the house). I was looking at this:
Amazon.com: Dual Digital Media Receiver with Bluetooth, SiriusXM Ready and 7 Channel NOAA Weatherband Tuner with Two 6.5-Inch Marine Speakers (AMCP5��BT): Cell Phones & Accessories
Since my tractor is outside (and it's wet here) a marine-grade system would seem to make sense (though it's inside the cab- my experiences with cab leaks tends to make me a bit hesitant to trust that things will stay dry).
I'm not sure if I really need the weather band functionality. It includes speakers, which I wouldn't look to install unless I thought they were needed: in order to seal up a cab leak my dealer used RTV on it, so popping that cab top off isn't something I'm really wanting to do unless it's necessary.
Funny, my dealer offered me a stereo to mitigate a delivery snafu/delay: said it was a $200 value :laughing: I declined because I wanted bluetooth. Also told him that I'd reserve the favor for a more pressing issue.