I did this myself. It was very easy I think. Use this guide and follow to step 3. Remember to move over the parts missing on the new part.
You could look at this guide to replace mid frame. I think you will understand which parts to move over. The battery is glued to the logic board and is very easy to get out.
The clue here to ensure the X3 Compact is waterproof again is to seal the back cover right. There are some original Sony adhesive on Ebay for the back cover so I ordered it also. I thought maybe I would have to use that instead of the adhesive that was on the OEM back cover I ordered. In fact I did not use it (as was recommended from some posts).
Be sure to clean any left over adhesive from the frame where the back cover sits. Use some alcohol to clean the edges. Then remove the adhesive film and seat the back cover. Use a heat gun or hair dryer to heat the edges. Put pressure on all edges until it cools. I put som heavy weight on the phone to make sure it sealed while it cooled.
To test if your Z3 Compact is waterproof do this:
Dial this from the phone -> *#*#7378423#*#*
Got to -> Service Test -> Pressure Sensor
Press gently on the screen while all the flaps are closed. The pressure rises and if you let go it will fall back to the atmospheric pressure.
The first Z3 C I changed the back cover on I did not do the heat gun thing and the pressure test failed. So I thought I had to use the original on the second phone I repaired. But I tried the method above and the pressure test was successful without the extra adhesive.
Hope this helps!