Sorry to hear about your Renal mass.
Let us discuss about your query on the lung lesion. You do mention that you have a history of chronic cough
. For a 4 mm nodule, there is no imaging that could tell you if it is metastatic or not. The only way would be to take it off. But again for a 4mm nodule, doing an additional lung procedure would add to your hospital stay and expenses. The history of chronic cough again adds to the odds that it is not a metastatic lesion. Though I am not able to provide you an exact figure, the incidence of metastases in a 3cm T1 lesion is low.
I would concur with your surgeon. Currently concentrate on the renal mass and its treatment. You could get a repeat CT examination in 3-6 months time to monitor the lung nodule. If the nodule stays the same size then it is reassuring.
The reactive node means that it is draining some area of infection and hence enlarged - a finding again in favour of the lung nodule being infective.
Close follow up is the best option that I see in your case.
Hope it helped you.
Regards and Best wishes.