I do not use STI, can't comment on the different brands or models or years of production from experience. But, if I was shopping for new STI, I would start a conversion about the merits of Campy, Sram and Shimano with bike mechanics in every nearby shop. I also would lean towards ones that can be rebuilt.

Gravel touring, I was unhappy with my 700cX37mm tires on gravel so I bought a 26 inch touring bike for the trips that are predominantly gravel. I have used that 26 inch bike with 40mm wide Schwalbe Marathons (with GreenGuard) on pavement touring and was very happy with them. I have also used that bike on gravel tours with 50mm wide Dureme tire on the front and Marathon Extreme 50mm on the rear. (Unfortunately the Dureme and Extreme are now out of production.)

I have cantilever or V brakes on all my bikes, can't comment on disks. I prefer cantilever over V brakes, if you are using STI I suspect you would be much happier with cantilever than with the travel agent adapters on V brakes.

I agree with the others, if money is no object you should get the S&S couplers. But unfortunately that means you should carry an S&S wrench (in the event that they loosen) in your on-bike repair kit wherever you go. I put a piece of electrical tape around each end of the coupler threaded piece to keep dirt and dust out of the threads, that helps keep them from loosening, but I still carry a wrench with me.

You were silent on luggage, if your new bike comes with panniers, I have never heard anybody complain about Arkel. I use Ortliebs, but if someone was going to give me a set of my choice I would probably pick Arkels. I have toured with someone that had red Arkels, they faded in the sun badly, if you get Arkels, ask around what color is least likely to fad.

For all components, think about long term reliability, ease of adjustment and ease of maintenance. Everybody seems to be on the more is better fad for number of gears, but I am quite happy with 8 speed chains and cassettes and triple crankset.