You will LOVE the 4212. I have the 5215 and love it even more!!
Autopilot:
Garmin does now have AP's. They purchased TR1 last year, who made one of the best AP's available. They just released the GHP10 AP, which is the old TR1 system, upgraded a bit with a nice color LCD display, some better configuration software, and some other nice additonal features and fixes.... The price is right, and Garmin does an awesome job with software, so I'd bet it will be a knockout unit. Haven't got mine yet, will purchase and install in the next month or two to be ready for next season.
That said, pretty much ALL AP's are compatible with all chartplotters, as long as they both have a NMEA input and output, they will work together.
Radar:
Regular radar VS the newer HD radar's is simply like comparing an old 480 x 320 color monitor, to a newer 640 x 480 monitor. A bit better resolution, clearer picture.... but they both get the job done. the bigger the dome, the better, so buy the largest dome or array you can afford, that fits on your boat. All you need to know about radar basics:
http://www.thehulltruth.com/forums/t...ode=1#M2286400