Rear Calipers for 2016 Mazda Cx5
I have to replace my two rear calipers because fluid was leaking out of the boots where the piston comes out to meet the brake pad.
I have a list of questions that hopefully can get answered by this community so that way I can make the best decision.

Purchasing the parts
1. Can I trust third-party sellers to sell me OEM parts?
If so I was thinking about going through Rockauto or Quirkparts. Also, any suggestions that I did not list?
2. Is it fine if I just buy the piston body since that was the only thing that failed?
3. Do I need to buy a new Rear Parking Brake Actuator?

Replacing and assembling
1. Is there anything I need to do before pairing the new rear piston body with the old Rear Parking Brake Actuator?

Please feel free to add any insights on past experiences that helped you get through something similar.

I will also document the journey of me going through the steps and problems I encountered.

Thank you!