I can only offer info on what I was told and mine is not kidney.

Was told biopsy confirms it. They have an idea from what they can see on scans- cancer looks a certain way however they can only suspect. They normally operate if that's first treatment option and at that point they send off and examine the cells tissue to 1)confirm cancer 2) grade/look at what type it is etc this is when you'll have better idea of longer term plan. 
this is what I was told by my oncologist. Apparently most cancers have a standard treatment option so for instance suspected cancer in isolated area such as kidney or ovary there is generally a recommended treatment often conservative which is to take it out.

You'll have much better plan with the specialist as they will be the one performing surgery/treating you and more experienced. You should be given a nurse to offer you support and answer any questions. Having been in this situation sometimes having a plan helps a lot although appreciate it's a shock. 

Fingers crossed for you it's simple procedure however do reach out for support there's lots available and it is such a difficult time.