This config does not make much sense to me.

Does Rene Herse even make cranks? I thought they only made frames. And which double crank? 53/39? 50/34? Neither?

And downtube shifters? What is this, 1970? :facepalm:

My 2c:
* Frame matters only to the extent that it needs to have clearance for 700x28's and fenders. And even that applies only if you routinely rando in the rain and/or off pavement. I would not go chromoly unless I absolutely had to. If you weigh 300+ lbs, you might want to consider chromoly. If not, stick with aluminum till you can afford carbon or titanium.
* Get clip-on aero bars.
* Make sure that you can hang 4 bottle cages on the bike. This normally means 2 on the frame and 2 behind the seat. (The alternative is to get a Camelbak, but I think that it's better to keep heavy stuff hanging on the frame than on your body. Some people get handlebar-mounted water containers.)
* Since you're going mechanical (and Di2 seems outside your budget anyway), there's absolutely no reason not to get a triple crank.
* For LD events longer than 300k, it's highly recommended to have a dyno hub. It'll weigh a ton (ok, not a ton, but it adds about 1 lb to your total weight, vs. a standard front hub), but it is useful because you get to the point where all your electronic equipment, from Garmin to cell phone to lights, runs out of juice long before you're done. You can keep Garmin powered a bit longer with an extended battery pack, but you want a dyno hub to power your lights.

Finally, you need to spend as much time thinking about the accessories you're going to carry with you, as about the bike build. Far too often people spend hours agonizing about Shimano vs. SRAM drivetrain but only give a passing thought to the stuff that goes into the saddle bag. In randonneuring, one of the key objectives is being prepared for emergencies. Can you fix the bike if something goes wrong? Can you fix a flat? Can you fix two flats in a row? Will you be able to get home without calling your SO or a taxi if you fall off the bike at 20 mph?