The Tandem Cycle Works folks know their tandem stuff. There will be no bickering on price but maybe a free rear rack or some bottlecages? Or a deal on last years model or a demo that fits properly.
Get to test ride as many models/brands as you are interested in.
S&S is an expen$ive, and perhaps unnecessary, expenditure unless you will take a multitude of airplane trips. Even today folks have been charged for S&S tandems packed in suitcases . . .
A carbon forks will be a plus; a full carbon tandem would be even nicer.
Suspension seatpost may not be needed on steel or c/f bike; however on aluminum it almost becomes a necessity
Would not suggest to do the Triple Bypass as a first time century as tandem newbies.
Have ridden 325 miles in 3 days with 22,000+ feet of climbing, finishing at 103 degrees in our younger days (were in our late 50s then). Stoker did not wish to repeat that event the next year (it snowed anyway), although she has over one hundred centuries to her credit.
As for equipment . . . Ultegra is pretty well D/A from a couple seasons ago.
Brakes? Would go with V-brakes with *option* for either drum or disc, in rear only.
In our 225,000+ miles of tandeming, we have ridden down some long twisty mountains with only canti brakes; with V-brakes; with caliper on front and V brake in rear. All worked fine.
Heck, for a first tandem you could be better off buying a good used one; after a year of riding you'll be a lot more knowledgeable and know what you like/dislike.
Buying a tandem 'just once' is like saying: have sex . . . 'but just once'!
You control the purse, you decide!
Good luck.
Pedal on TYWOgether!
Rudy and Kay/zonatandem