Though I think these dolls have become much more common in recent years, BJDs are still a niche hobby, and as such it fares much worse when it comes to information decay. Language barriers, and the death of many forums, and the size of the companies (or lack of size) makes information about them harder to find the older and less "important" it is. I'm very interested in the less important aspects of things, so whatever crumbs I find, I'll put here.
Most companies or individual artists that produce BJD don't have any sort of physical store, so aside from the occasional doll event, you pretty much can't learn anything about them that isn't explained on their websites. It's hard to even know exactly how many people are working for a company, and how many dolls they're actually selling. Social media has changed this a little, but not much. So finding information about the people behind the dolls, or their creative process, is really a special treat.
LUTS is really well-established at this point. Here is most of the relevant information. I think a common, very important question that comes up quite often regarding LUTS is how LUTS is even pronounced. If it's written like Luts, obviously it rhymes with "puts", right? Wrong. LUTS is actually an acronym for Loyalty, Utility, Trust and Service, pronounced loots. I think that's kind of cute. It seems this information is currently only available in the guide booklet.
Kinoko Juice キノコジュース
Kiki and Jill can't sit down all the way, but Kinoko Juice is without a doubt my favorite doll maker. Kinoko Juice is a duo comprising Kame and Codi. I'm unsure of their relation but they've been creating dolls together for a long time. I believe Codi makes all of the dolls by himself, so up until they opened their own online store, Kinoko Juice dolls could only be obtained via online auction and special events! But it's still a small operation, and you usually can't preorder your choice of basic doll and wait a few months for it to be delivered, which is typical of doll companies. What they have available is what they have available and you can pick from that.
Kinoko Juice puts a lot of effort and care into packaging the dolls cutely. I think postcards are quite common, but I've never received a keychain before!
Foveo is a Korean doll company that primarily produces mature mini girls. Samieru, the doll maker, has a unique style that isn't seen much from other companies. The faces she sculpts are very round and soft, balancing cuteness and elegance perfectly. She's also very good at sculpting hands.
Foveo dolls are an unusual size, but they fit right in with Model Delfs. So even though there aren't any Foveo boys yet, Model Delfs make pretty good boyfriends.