Re: Seiza pain?
None of us can diagnose it from here - could be tendon, fascia, pinching nerve, who knows - , but you are absolutely right to stop doing seiza until it heals.
In general it is pretty common for folks to develop various foot, ankle or knee pains when first doing seiza. Most people don't do any real harm to themselves and are able to slowly condition their bodies for it by starting w/ minimal time in seiza, doing lots of stretching after warmed up, and slowly increasing the time.
But if you have an experience of the pain actually progressing into other activities, you have created an imbalance or acute injury that needs to have a chance to heal itself.