The one difference that medical studies have found is that people with seronegative rheumatoid arthritis seem to have less overall joint erosion and damage than people who test positive for the antibody, and usually do not develop nodules under the skin, as the positive group tends to do. Otherwise, the symptoms and progress of the disease appears to be similar in both groups. So, if you test negative for the antibody, you will still likely experience joint swelling, stiffness, and damage, but not to as great a degree as those who test positive.
Plaquenil is a fine medication to start off with. I've been taking it for a number of years, along with sulfasalazine and a low dose of prednisone. It's a relatively benign RA drug, normally without many side effects. However, in rare instances, it can affect your eyes, so you should get an eye exam soon and every 6 months to 1 year thereafter. Also, plaquenil can take up to 2 months to fully kick in, so don't get discouraged if you don't feel better right away. If the plaquenil doesn't help you enough, there are lots of other meds to try.
I hope you'll keep in touch and let us know how you're doing and you are always welcome to ask questions, make comments or just stop by to say hello. We'll always try to help!