You might find some info inside the following AMA weblink that may be of help b4 you leave for your trip:
I'm assuming that you've had the driveshaft splines checked at some point--given the number of threads on this website about this subject. If they are dry, and you leave home on a trip of that length, you could be on foot b4 you get back.
On a trip of that length, on a used Vulcan 750. with 21k+ miles, I wouldn't think of leaving without some way of monitoring the health of the charging system (i.e., a mounted, water-resistant, shock-resistant voltmeter).
How do you brakes look? Front pads look ok for a while longer? The rear should be holding up ok, most likely....
How long ago were your clutch, throttle and brake cables lubed/serviced?
The stats show that the most likely thing in your electrical system to fail is the BATTERY. Have you had the battery tested--if it is more than 2 years old?
You've been made aware of the "phantom gas syndrome" I gather, so you should know what to do if that happens, too.
In case you weren't already aware, you have power leads in your headlamp bucket that can be used as a power tap to power/charge your cell phone...
On the way back, I'm hoping you can take some pix to show of the Beartooth Hwy, and some of the Black Hills around Sturgis (e.g., Mt Rushmore). If not, you'll miss some of the finest riding in the lower 48...