The digital crop factor makes choosing lenses a bit tricky. You kind of have to work backwards from film.
I think you need to start with two questions, keeping in mind you'll only have one lens (until you buy your second):
1. What's my ideal 35mm-film focal length?
2. What's my budget?
Then look at the handy focal length converter on the back of your R-D1 and pick the cropped focal length that comes closest to your ideal film focal length. Then try to figure out if you can afford it. Then figure out if you have to compromise, either for budget or handling reasons.
RF for me is primarily working close and tight, so I need wide angle. I almost never shoot over 50mm on a film rangefinder, and I rarely use a 50mm. If I only have one lens for a film RF, it's going to be a 35mm.
On an R-D1 that means something between 21mm (32mm equiv) and 25mm (38mm equiv), which is a more expensive range than 28mm or 35mm. The cheapest is probably a used C/V 25 LTM, but that isn't rf coupled, which I find a pain. The M-mount 25mm C/V is rf-coupled, but pricier. In 21mm you have used C/V, used Kobalux/Avenon, and used FSU (20mm, not RF-coupled, maybe won't meter?).
If the budget won't stretch for a 21mm>25mm, the next step is 28mm (42mm equiv). A little tight for me, but I could live with it. My first rf was a Minolta CLE w-40/2.0, and I used that one lens for a few years. 28mm gives you more options, both modern and vintage.
The most/best bargains are clearly 35mm lenses, as long as the focal length works for you. 53mm on film is way too tight for me most of the time, so I'd be unhappy with a 35mm as my only R-D1 lens. But that might not be the case for you.
The C/V 35/2.5 is indeed a fine lens, and priced affordably used. You can also find vintage Canon 35s on the cheap, as well as FSU lenses. Some find they get more digital dynamic range from lower-contrast vintage lenses...
Good luck with the search!