For a 70-year-old man who was recently diagnosed with bladder cancer, is BCG a reasonable 1st treatment?

Maybe. Bcg is a first good step but depends on the biopsy specimen. Bcg is standard treatment for certain types of bladder cancer and if the patient meets those criteria, then it is a good first step. It is not necessarily dependent on age.
Depends. Bladder cancer should first be removed as much as possible through a scope placed through the penis and urethra into the bladder. For small tumors that have not grown into the muscle, either bcg or chemotherapy placed directly in the bladder is usually recommended to try to kill any remaining microscopic cells and minimize the risk of recurrence. More advanced tumors need different treatment.