1) The reason I ran power to the RD from the fuse box is that my radar detector (Valentine 1) has a separate power module which I have run accessories from (remote display and remote mute button) so I would have to run either 2 wires up or 4 down. I chose the 2 up.
2) I used 14-16 gauge (blue) "T" type wire taps, but any type will do fine as long as they are 14-16 gauge.
3) There are some free slots in the fuse box you can use. Here are 2 that I have used:
I used the wire and fuse supplied with the detector. I don't remember what they are exactly but I am sure you will be fine with 16 gauge wire and a 2 amp fuse. You can also see in the photo the ground on the bolt to the right of the fuses.