There is a lot of advice and information on NRAS website, the national RA charity. They have many booklets which can downloaded free (although you have to disclose some personal data before accessing the ‘basket’).
Also, on Mumsnet, check out the ‘Autoimmune Disease’ topic, rather than this ‘Chronic Pain’ one.
As another poster says, the initial appointment will be a more thorough assessment as well as seeing a Rheumatologist (Consultant Doctor). I had to strip off for a gown (ie with only my knickers left on) examination which I was not expecting at all and needed help to get undressed, etc., so perhaps you need to consider this for what you wear, bearing in mind your pain levels. Also, you may have to undergo X-rays and scans, etc. Nothing invasive other than blood tests, though.
It is no use speculating about your diagnosis until you have your appointment, but I would read up only the basic info. (on credible sites) which will help you to formulate any preliminary questions. Once you have a confirmed diagnosis you can then read up and access lots of information about your disease and the medications, etc. and go back to your follow up appointment armed with relevant questions.
In other words, try not to overwhelm yourself with lots of information which may not even be relevant, depending on your diagnosis, as there will be other opportunities to ask questions. Spend these few days thinking about your medical history and make a note of when key events, symptoms and pain levels occurred as these will be among the questions they have for you. Check your family’s (parents and siblings) medical history too.
Hospitals vary in the way Rheumatology patients access services, so again, wait til you know what you’re actually dealing with and then you can seek support elsewhere where I suggested at the start of this post.
Good luck and I hope you come back to let us know how you get on.