I was going to suggest walking in the dealership with a wad of cash (literally) and make a deal. works for me. I am lucky enough to be able to save up for my major purchases and it really saves money in the long run. A credit card alone cost the dealership 3% of the purchase amount. That is $360 on a $12,000 purchase.
So buy either buy a new (out of the box) Tenere (2014, 2015, 2016) or a loaded previously owned Tenere of the same years. Go to the dealer prepared to purchase. Do your homework. Know the rates. Know the prices. Have evidence for anything you state. Four years of YES can be had for less then $400. Do not pay more. Purchase from a dealer that you trust in the garage. This is a business deal. Treat it like one.
If you ride off-road a lot OEM Luggage can be a concern. Cost me $400 on one tip over. If you ride mainly road then OEM Luggage is nice since it fits tight, less air drag, and looks very nice, the cases and mounting hardware are light in comparison. When traveling I use one insert for everything I will remove to take into the motel/lodging and leave the other side case filled with what stays on the Tenere. I don't have a top case but the riders I know like it. Sort like a girlfriend... whatever works for you.
Engine guards (crash bars)... difficult to beat Altrider.
Exhaust... whatever works for you. I have had an Akrapovic for more than a year and haven't installed it.
Skidplate... ACD is a tough plate that protects a lot. Jaxon makes the ultimate engine guard/plate.
Accessory Lights... again, whatever works for you.
Windshield (Gen2)... many different windshields available. I have the OEM Touring windshield and like it a lot. Usually run it in the low position.
Windwings... the OEM Windwings are a good thing especially during winter riding.
Accessory Bar Bracket... prevents the windshield and accessory bar from bouncing. A forum member makes them and sells them for a reasonable price. This should not be an after thought.
Seat... read read read.
Rear Rack... again Altrider makes a very good rack.
Horns, Foot Pegs, Sidestand Big Foot, Rear Brake Slave Protection, Final Drive Coupler Protection, Fork Seal Protection, Handlebar Risers, Handlebars,... read read read.