Run a line of caulk adhesive along the top edges of the vanity cabinet and place sink on the top pressing into place. This is a rectangle sink with a flat bottom. If you get something similar make sure the sink is leveled correctly to avoid improper draining and pooling in the sink. Read reviews when purchasing new items. It is very helpful to avoid problems people have had.
Reinstall the toilet using a new wax seal.
If you had to cut any part of the wall to make the sink fit now is the time to fix that with new drywall where it was damaged.
If you don't have experience with any plumbing you could hire a plumber in install shower and sink fixtures. I did it myself. Follow instructions to avoid any leaks. Again, not something you want in a reno project.
Tip - Take a picture of the pvc pipe before you remove it. That way you can reconstruct it after and avoid purchasing new. You will need to clean it very well. It will be massively gunked.