Here's my advise, and sorry it is so scattered:
For late afternoon with good golden light, I would not bring a tripod. It can inhibit you, and handholding often means more creativity. I'm not against tripods in general, but having shot weddings for years I rarely use one. The flash goes a long ways to mitigate your hand held movements and your subject's in most cases, and of course a fast enough shutter speeds does that even more. Start with ISO 100 and make faster as required, but I suspect 100 or 200 will be enough.
For all your compositions I would strongly suggest fill flash. All of them. Nothing worse then a great comp, great background with under exposed faces. Fill means you are better able to balance background light with the light reflecting off the subject's faces.
I would strongly advise against a non-Nikon flash, or make sure the non-Nikon flash plays ball with your camera's iTTL logic. If you use a recent Nikon flash, it will use the camera's TTL logic to get you the exact fill power you need, so don't stress how to set up fill....let your Nikon body and flash worry about that.
Shoot in Av mode, and try not to get the backgrounds too sharp as that could distract the viewers eyes too much. Go for the creamy background bokeh, and of course their eyes should be very sharp.
For under $30 get a flash frame. It will be VERY helpful.
Shoot raw only. Go with auto-WB knowing you'll have to dial in the first picture of a given set during raw conversion. Optionally you could dial in the WB with the first shot of a set by using a white or gray card...make sure the monitor you'll use to post process is calibrated!
Convert in the raw images in the biggest color space you have, and at 16 bit color depth. Why 16 bits if your raw is just 12 or 14? 16 makes room for math rounding; the math your post processing program does when you post process. Doing so minimizes blocking, combing and other digital artifacts.
NEVER add sharpening to the entire image, and never add sharpening until the last step before you publish/print the image. Apply USM as the last step and ONLY on the subject's eyes, teeth and other areas that really need it and NEVER on the bokeh. The application of sharpening via the use of a layer and mask means you can apply it surgically.
Have fun and keep it light, because the subjects will often mirror your mood. Get them to laugh.
Try not to frame every single comp square...meaning, try tilting the frame but make sure it looks "intended" and not sloppy. Go on the internet and print out dozens of engagement poses and bring those with you if your memory is not the best.
Ask the subjects to try to stay clear of solid bright colors. Bring a friend to help you carry stuff and set up the shots.
And remember you are not just the photographer. You are also the director, so do direct, give direction, and of course stay open to their requests too.
Report back and show us your handiwork!
Good luck