Average dose of nolva is 10 - 30 mg/day
Personally, with the amount of gear you are running, your chances of gyno are very small, although dbol might aggrevate it. Unless you are very prone to gyno, i wouldnt worry about it too much, and only take nolva if signs of gyno appear.
Personally, if gyno does appear, just drop the dbol. But since you are only running it for 4 wks, your risk is minimal.
Good luck and grow