Our infield starting player defense was generally mediocre to bad, with 1st base being the strongest of the lot. I agree with your assessment of Pedey. He was great, but time and injuries have left him a part time player and he skills are diminishing. Bogey is a serviceable SS but not a great defender. I have hopes that a different hitting coach will work closely with him too rework his swing and plate approach. He is 6'1" and 210 #s. He should have more power but needs to make changes to realize his offensive potential. i am hoping that will happen, but only if Bogey would commit to make changes.
Devers was a major defensive liability. Your concept of having play winter ball at 3rd base is one way to see if he can make the improvement needed. His hitting is already fine. A secoond approach would be to assume he will mature into a heftier player and move him to 1st and have him learn the position over the winter. So we need a Nunez type player as a minimum and a 1st/3rd base power hitter. Beyond that we need to be open to alternatives.
So basically in the infield we need help at 2nd, 1st as Moreland probably won't return and Hanley is not a full time 1st baseman. SS is questionable and probably isn't a priority and 3rd may need some help depending on how Devers is handled. i agree that the catching position is solid with Vaz. Leon is a good backup but might be replaced if the opportunity arises.
I agree that the pitching is okay and we have the pieces to go forward. Whether Price's elbow stands up to the rigors of a full season will remain an open question.
The outfield is another question mark in my mind. We have a very athletic group there now. Beni showed his youth in a lot of defensive throws that weren't so good, but otherwise we were very good defensively. JBJ is a very erratic hitter though and we wound up with him hitting 9th for a reason. He will turn 28 at the beginning of the 2018 season and has had the experience to define who he is as a hitter. I don't see him improving and would consider a trade if we could find a better player. Mookie could shift to center if needed and we could either add a CF or a RF. If we would spend the money, there would be some interesting candidates for the outfield.
Utility positions need a complete reset as do some of the coaches. Whoever the new manager is will determine who he wants for coaches.