Hello,
Thanks for the query.
1. Enlarged nodes are commonly due to infection, inflammation or rarely due to cancer. Routine blood tests can be normal in such cases. Possibility of cancer seems less likely, as there would have been associated cancer symptoms by now. If you are concerned getting it checked with an ultrasound scan / fine needle biopsy will reveal the true nature of this lump.
2. Since you have pain in the rib and mid back region, I think possibility of chest infection should be considered as first possibility. A detailed chest examination and chest X-ray needs to be done to evaluate this.
3. Enlarged xiphoid process without any symptoms does not concern me. It is also not related to the nodes in your arm.
4. In my opinion you need to consult a general physician / chest physician. The doctor can tailor investigations for you after clinical evaluation.
Hope that answers your question. Let me know if you have any other concerns.
Regards