Is this hard to do what adapters if any do I need? Should I get it professionally installed?
This exactly. I did it myself. You can go a ford dealer and get the wiring schematic for the back for your stock deck.All you need to do is you need a sub amp that has high level inputs.You will need to run a good quality Red + power cable.I ran one right from my battery back to my trunk.
This will take you the most time.You can also include a proper size fuse for the
amp in the wire.
You will also need a ground cable,this is easy you can
use any part of the metal body of the car.You then just tap wires from your rear speaker output into high level inputs to the sub amp.
Do searches its not to hard, if you take your time and read up.
Also before you do anything disconnect your battery.