Radio wise best to follow the power it through battery and a proper ground. Fire wall the vehicle service manual should have it. They are usually easy to spot rubber deal. Commonly one is located near steering column path and to left. Ford tends to have them on passenger side as well but ymmv on its location. Just be careful you don't prod into existing oem wires they tend to cram those in unless they have a separate grommet that is empty which is bonus.
I would also suggest running a small conduit through it for future wiring or have a couple decent wires dead and ends protected so if you need to run anything else it'll be easier in future.
I wouldn't tap into anything with a radio and if you have to use ignition sense use the proper fuse or a non critical slot with fuse adapter ideally a empty slot but sometimes this isn't possible. But definitely wouldn't run it off a critical fuse slot.
There should be service manuals online of the grommet locations and firewall access. Here is a video of a 21 but should be close in locations as they usually are.
A couple reads suggest the left side by driver area is easier place to run through.
Vehicles like this are great where you can remove easily items in engine compartment to run and have room with minimal tear down if you got big hands and arms.
Also don't forget to protect the wire in engine compartment and not running wires over any airbag paths. Specially if the front driver area has one equipped under steering column area. You'd be surprised how many forget this running wiring.