Not long. In general, observation of 8 cm kidney cancers (renal carcinoma or rcc) is not common, except in extenuating circumstances such as poor health, very old age, etc. While chromophobe tumors are generally less aggressive than conventional rcc, tumor removal via partial or total nephrectomy should be considered carefully to avoid potential progression. Tumor size is associated with this risk.
No one knows. I am assuming that you had a non-aggressive eosinophilic chromophobe kidney cancer completely removed. I was unable to find survival curves but the vast majority of folks like yourself don't have problems after, and it's your urologist's call whether to do follow-up imaging. I'd rather be in your situation than be diagnosed with high blood pressure. Congratulations on a likely cure.