Your tendon and sole of feet issues (this is plantar) are enthesis; inflammation of the insertional points of the tendons to bones. Enthesis is seen almost exclusively in the SpA's such as psoriatic arthritis and IBD arthritis.
RA is very much about redness and swelling even early on as are most of the SpA's. Reactive arthritis and IBD arthritis have a propensity to present as an arthralgia without swelling since by their nature there is limited, if any, inflammation present with the immune system overreacting to another stimulus.
RA tends to be symmetric but early on this may not be as noticeable. The SpA's do not tend to be symmetric (especially not psoriatic arthritis) but it would not be unusual for a general polyathraglia to exhibit some form of symmetry. The SpA's will also have eye, nasal and even sinus issues whereas RA tends to not.
This is interesting Damo123. I've recently developed pain under my foot, which I suspect is some form of tendonitis or plantar fasciitis, and have a persistent problem with my shoulder (rotator cuff) that shows visible thickening on ultrasound scan. As I have psoriasis a diagnosis of psoriatic arthritis wouldn't surprise me. As I said in my reply to Simon in another thread, my aim is to switch to a new drug that'll treat the UC and joint problems (as Humira seemed to be doing till it failed for UC).