at L5/S1 grade -1 can be managed by Physiotherapy
if pain is tolerable and not chronic.
2. If pain is intolerable or persistent despite adequate rest or if associated with numbness
/ weakness in lower limbs
etc. then it warrants surgical correction.
3. Yes, after surgical fusion of the segments you can continue your day-to-day activities. Sports activities might take a bit longer period still the fusion is complete.
4. Back strengthening exercises with rest on hard bed might be useful to decrease pain. Avoid bending the back, leaning forward, lifting weights, prolonged sitting in same posture.