I got my F90BT from Ikesound.com for less than $900 - great price.
This and probably other units are a bit more complicated than I suspected. I installed new speakers/amp/HD radio/and a rear view camera. Like you it has been a while (cassettes were the latest) since I had worked on installing a system. There are several key connections needed - Speed sensor, reverse gear wire (for automatic switching to rear camera mode), microphone, GPS antenna and the by-pass (if you are so inclined). I had already purchased an OEM service manual for my Honda Ridgeline and without it I would never have been able to pull all the interior panels apart without destroying them. Speaking to just the head unit install:
Speed Sensor (VSS Variable Speed Sensor)- Thank goodness a fellow Ridgeline owner posted photos and wire colors - had to connect a wire to the stability control unit (each wheel has a speed sensor) the info was in the manual - once you know what to look for. Easy for this rig since the unit is on the side of the front passenger wheel well
Reverse indicator - got lucky with the wiring diagram showing the wire color of the lead under the dash for the backup lights and confirmed with a multi-meter.
Microphone - I ran the mic wire up the A-pillar and under the headliner along the wire harness for the lights and use the provided clip to position it on the headliner just above the rear view mirror where it seems to work fine and is not noticeable
GPS Antenna - improvised here after seeing the OE version was mounted under the front dash - a magnetic base is provided and I used some 1/8" flat steel braces from ACE hardware for additional stiffness and basically duct taped it to the UNDER side of the dash - I haven't had any reception problems
Other Notes:
Lots of Zip ties
Remote steering wheel controls - there is only one company that I found that makes a remote converter and I ordered it through Crutchfield - directions are terrible, I spent several hours attempting to program it - took a break for a couple days and was looking at the OEM manual and noticed there is a ground wire on the head unit harness for the steering controls - After connecting it (which was unconnected with the new adapter harness) to the converter ground (any ground may have worked) the programming seem to be accepted - but I'm still working on it.
Antenna Lead - No one makes the necessary splitter - The HD radio takes the antenna lead and provides the signal for both the HD and standard radio, but to use MS Direct service – which is free for 3 months - it needs an antenna lead into the unit. Found a Y splitter on ebay for ~6 bucks w/ shipping and bought a generic 4’ extension cut off the female end and installed a male connector (cable needed to have two male connectors from the Y splitter to the head unit).
Everything on the unit is operating (HD radio, standard radio, MS Direct, backup camera, I-pod, and GPS) but it is still not quite right. Camera does not come on when placed in reverse but does display after starting the car or when selecting it from the screen (I have checked and changed the camera polarity). Down to the final few items – worse case I take it in to a shop to find the problem. All the connections they may need to check are in place and easy to get to, I would expect the cost to be minimal, but I haven’t given up yet! Good Luck