There are numerous WoB about Roshar's solar system!
Roshar is a very different planet in terms of the cosmere. It is inhabited by three Shards, more than we know of on any other planet. It is part of a solar system, named Greater Roshar, that actually has multiple Shardworlds in it.
I don't think we have WoB on the order of the planets, but in terms of importance, Roshar is first. It has three moons, which cycle every night. They are Salas, Nomon, and Mishim, and appear in that order every night on Roshar.
The next most important planet is Braize. This is referred to by Rosharans as Damnation, but I don't believe they know that it is an actual planet. Braize is where Odium is in present day Roshar. Beyond that, we really don't know anything about the planet, but it will become more important as the series goes on.
Least important right now is the planet Ashyn. This planet is not inhabited by a Shard, as far as I can recall, but it does have some Shardic influence. Brandon has written a book entitled The Silence Divine set on Ashyn. He eventually intends to rewrite and publish this one. As far as we know, Ashyn will have no significance to the Stormlight Archive.
I am not the most literate in theories, but I don't believe there are any significant theories pertaining to Greater Roshar.
More information on these topics and similar ones can be found on the Coppermind.