Clint, in the past, I used to do quite a few weddings. I just try to stay away from them now, though I just took one on in September on Labor Day weekend. That will likely be my only one this year, and it will require an assistant. I'll hire a student from the local University of the Arts, as I've done before.
I wanted to comment on your post. This wedding starts at 7:00pm. The OP is from Kileen, so I assumed nearby Waco to get the Sunset/Golden Hour numbers. I also used April 15th since the OP said sometime in April. On that date their Sunset is at 7:57pm, and the Golden Hour starts at 7:24pm.
That means that by the time the wedding starts, it's already pretty darn low light. When I've done weddings, outdoors, under such conditions, while I have some light, it's not enough to get nice crisp photos of the faces of the people at the wedding and the participants, especially the bride and groom.
Despite the utterances of the bride and groom (I always especially listen to the bride, because unless this is an unusual couple, down deep it's her day and he's along for the ride.) concerning the "christmas lights and (sparkles), they want to show up in the photos, if their faces aren't spot on, even if the lights and sparkles look great, they will be greatly disappointed. When all is said and done, the memories are going to be the faces of everyone there, not how great or bad the lights look. The bride and groom just might not have figured that out yet. As I mentioned earlier, it's unlikely, even with great manipulation, that both will look great at the same time.
So getting back to the light, even at the beginning of the ceremony, I'm willing to bet that at the least a fill flash will be essential to show off the faces in the photos well.
That late I've used fill flash on every wedding I've ever done, and eventually moved to predominate flash to light the people. If done well, even right at sunset, you can handhold the camera/lens and still get wonderful shots, which use ambient light, plus flash. (Actually, even earlier in the day, I'll likely use fill flash. I did an event yesterday morning through early afternoon. I used a fill flash all day long as faces were paramount, but the rest of the photo was important too.)
So below, please find a sunset shot at a west coast afternoon beach wedding I did. The bride and the groom love the shot, and I can't tell you how many copies of it and variations of it are being used by destination wedding travel agents for their websites.
The shot was taken using a D70 (Yes that old technology.) with the 18.0-70.0 mm f/3.5-4.5 lens set to 29mm, ISO-200, f/7, 1/200 sec, with an SB-800 flash on a bracket, set to i-TTL BL. I'm sure I was using matrix metering, no EV used.
According to the position of the sun, how the lighting is filtered at the location, etc., you may or may not be able to use solely ambient lighting at any time during the wedding, according to the max limit of ISO you want to use, though with either the D3S and D800E, 800 wouldn't be out of line, although, based on everything, I'd probably top it off about ISO=400 to ensure my blacks are beautiful.
Using a fill flash will keep the ambient lighting in the photo nicely, but enable the faces to look great, and keep the shutter speed up, even with the aperture kind of middle of the road to create good depth of field, which is a good thing to use during the ceremony.
I'd use the SB-910 Tom indicated he had, front sync, i-TTL BL FP (His cameras can be set for this and are both compatible.), matrix metering, Aperture Priority (A) (so he has depth of field control) and let the camera/lens/flash figure it out. If it's a bit off, a bit of EV will take care of it.
One final note, with a 7:00pm start, they've got just ~24 minutes until Golden Hour and less than 57 minutes until the sun is down. That means they don't have a whole lot of time to get through the ceremony, and have time for a few after ceremony set shots. You said, "About 10-15 minutes before sunset I'd settle in a place of where they wanted a prime photo taken form." That's a good idea, if they have the time according to the length of the wedding service. I've been at weddings with a 10-15 minute ceremony, and others over an hour. It's according to what they are having if that will work.
Whether it will or not, I'd definitely schedule the mandatory single, double and group portraits prior to the ceremony, to be complete between 45-30 minutes before the start of the ceremony, or maybe even further before the ceremony. I'd certainly be at the wedding site for the pre-wedding candids and posed candids, from 2-5 hours before the ceremony, according to what the bride and groom want and are willing to endure.
In my opinion, weddings are the number one pressure sport for photographers. You get one, and only one bite at the wedding ceremony apple. Miss and it's all over. Preparation is key. For outdoor weddings in particular, in my opinion, the photographer must be at the site on a day very close to the wedding and take test shots so the photographer has a solid idea of what to expect, and hope that the conditions are repeated.
I'm based in the east coast. When called to do a west coast wedding, or even a wedding closer, but out of my immediate area, especially if it's outdoors, I fly in 1-3 days before the event and go on site at least once if indoors, and twice if outdoors, during the time the wedding is to take place to take test shots which I share with the bride and groom to make sure we're on the same page. For outdoor weddings getting the basic exposure is key, and for indoor weddings the challenge is the white balance, which is typically a composite, and therefore custom white balances must be preset. I charge for the advance in the wedding's prepaid package price.