Is your baby eating table food? Eating plenty of baby food if not table food? If yes then take the 12 month WCM marker with a grain of salt. There isn't a magic day. You shouldn't give more than about 24oz per day. The idea is that by one year baby is getting their main nutrients from food. If your baby is not eating enough foods for you to consider it a relatively well balanced day of meals then consider formula if your baby is small or otherwise you have a concern.
ETA: I had no pain when I stopped nursing either time. I also never had any engorgement.
It's going to be different for everyone. It could be painful or not, you could become engorged or not, you could get a clogged duct or not... it just depends. I would just listen to your body and any new aches or pains you get.
If it's been four days already, it shouldn't be too much longer before you're in the clear.
It will be unconmfortable, there will be some leaking. try gerber good start gentle. drain the breast less frequently, slowly minize pumping...