For tge aerial converter you need a power feed which can be taken from the interior light.
If you get the correct loom and patch lead then the stereo functions on the steering wheel will work.
Fitting the stereo i would remove the r/h centre vent to give you access to move the cables out of the way when sliding the stereo in.
i purchased an RS Parts splitter and didnt like the way it held water on the lip if it rained or was washed. I then purchased another one (got it cheap) and decided to modify it...The Escort Cossie being my choice of inspiration....
Lip is flat
After - lip is at an angle from front to the rear
so, what do you think?
I even thought of adding some lettering and was going to put the new Focus badge on (in black) but then decided against it.