Well vitamin d is definitely not as strong as steroids. It's interesting you notice a lot of relief from it. I wouldn't worry about it suppressing your immune system that much personally otherwise there would already be a black box around buying it. There is a question of how much to take, I started taking 5000IU a day after I started getting neuropathic & inflammatory problems, and haven't seen much improvement. However, we don't know how much is valuable for people suffering from potential autoimmune diseases to take.

Some of the benefits of the antibiotics for autoimmune problems probably come from antibiotics natural ability to fight inflammation not through killing microbes. There are a lot of articles about this I'm on my tablet now so can't link easily, but minocycline is used as a disease modifying drug in rheumatoid arthritis. Some fringe doctors will also try deoxycyline to treat a whole range of autoimmune diseases. Some of them thinks it works because they kill microbes that cause inflammation, but it is more likely I think to be direct anti inflammatory actions on certain biochemical pathways. Certainly relating every autoimmune disease back to dysregulation of the VDR pathway is likely to be a over simplification as there will be a wide range of mechanisms. That said maybe all these people that develop gut problems before autoimmune diseases have some steps in common like certain microbes changing in number or permeability of the intestinal walls increasing. I don't think we know this yet.

Sorry to get on your back about paper quality, because in some sense, we don't know what the future will hold. However, I try and quality check journals I read when searching by looking at things like impact factor, citations, and the number of people in the study. Not necessarily to dismiss peoples work or theories, but put it in context.