Add a tripod to your gear. You'll want that for scenics in the area, especially Oxbow Bend. Autumn is a good time to go, late Spring is also good. You'll start seeing foliage color changes as early as September. I like GTNP, over YNP, for photography - although, you might want to spend a couple days in Yellowstone based on your trip length.
Lots of wildlife in the area, especially if you are patient and get out early and stay out late. A good area is the back road between Moose Jct. and Teton village.
If you want good early morning shots of the Tetons, get up early, and go about 12 miles east of Moran Jct., towards Dubois - a few small pull-outs along that highway. Later in the day, the light is too flat for good photos of the Tetons. If you want to get well-lit evening photos of the mountains, you will need to go over Teton Pass, into Idaho, then back into WY at Alta (ask locals for directions). You can get good sunset photos at Oxbow Bend, but the mountains will mainly be just silhouettes unless you do some HDR.
Another good area is to take the back road between Moose Jct. and the Signal Mountain area; you may even want to drive to the top of Signal Mountain - a good view of the area from there.
Personally, I wouldn't go with a guide service - but, then, I know the area fairly well. If you do get a guide, I wouldn't do so for more than just one day. The guide service probably would know locations of the various wildlife in the area.
Other than adding a tripod (or two), your gear list sounds fine. When I'm in that area, I keep the 150-500 on one camera, and the 28-105 on the other. You might have moose, bison, etc. be 100 yds. away, or right outside your car window.
4WD is a good idea - Wyomin' weather is quite unpredictable. Also take warm clothing - temperatures will definitely be in the 40's at night, possibly even 30's and 20's.
Have fun - it's a great area for scenery and wildlife.