How hard is this to do?

 

Like the op said, trim work is probably the hardest part. Then its just a matter of wiring it up to an add-a-fuse and tucking the wiring in. Alternatively to the version the OP used, you can also get a rearview mirror version. people have also added them to the visor i believe. Bunch of posts on it if you search it out

 

I just tapped it straight into the vanity mirror wiring. Should've used smaller connectors, because finding a place for them wasn't fun once connected. Damn, they glue that sh*t down to the headliner. I know they don't want it rattling around up there, but gees.