Is adding on to a fusion of l4-s1 more painful than the initial surgery? have to get l3/4 done and he said there may need to be revisions...

Unpredictable: the efficacy and complications of back surgery are unpredictable. They are an independent roll of the dice. The main determinant of how likely pain and other complications are to occur is how big the surgery. If one were very involed (like with additional steel hardware) and one were minimally invasive, the minimal surgery has minimal pain.