I have the 857D and have grown to love it. It's a great radio out of the box, but as a new HAM, it was a bit daunting to learn all of the features. I got on 2m fine and set up repeaters easily, it was just tough to remember what the menu setting was to raise transmit power or scan the band for strong signals, etc. Especially because the Jeep wasn't my daily driver and I only used it when we go on the road. Over time, I started putting together cheat sheets that related to the functions I used and liked. That really helped a lot. Now that I am using digital modes too, I feel pretty comfortable navigating around the radio.
As far as the ATAS... I looked at mounting that on the Jeep, but felt that I would one day rip it off with a tree branch or something. I have a dual bander for my local / highway comms. I also decided to get a buddipole setup. My logic was that I would probably never use HF while driving... if I made a contact, I would most likely lose it quickly while on the move. Plus, HF is a little more finicky as far as tuning... another thing I wouldn't really mess with while driving, even with an auto tuner like the ATAS. I found that setting up the buddipole is kinda fun once we get to camp and I can get a really good signal. The other thing I have found is that while a smaller (coiled) antenna is convenient (to include the buddipole), the more real length and height you have, the better (in most cases).