Medium format with flash and 35 with non formal shoots with some flash for fill or indoors.2 rolls for each format so people wouldn't pester you when you have finished.
OK. Not gear related but here's my two cents worth. If they want to have photographs worth keeping they should have a pro do it. You have never done one and there a lot of novelty shots and standard ones that will not occur to you. Folks who do weddings regularly get a rythym and they seem to just flow through the day no prob. It will be awkward for you and you may fumble through a bit so you might have some stress from it. If you have been invited along with your wife be prepared to spend the day apart from each other as, being the photographer, there ain't much time for socializing. You will view nearly the entire occasion through a viewfinder. It Is hard to participate that way.
That was all kind of negative, but if it is your intent to SHARE the day with your friends and your wife and enjoy yourself fully, leave the camera at home.
Given the relatively close range used with people shots and the likelihood of some biggish enlargements being requested I am surprised how few seem to vote for the Contax 645 as part of the line up. Pre d*****l most wedding photogs came along with MF for all the semi formal stuff and then those friends or relatives who were keen amateurs took the informals with 35mm later on and in the evening.
You have the best of both worlds in your camera line up. I'd use both formats.
Use the 35mm cameras for your candid type photos. When one runs out of film use the other and have your wife take care of putting fiim in the one just used. I'd use the Rolleiflex mounted on a tripod for family groups. No need to have another as this can be a slower time allowing for change of film by you. Have your wife use the 35mm cameras during this time as some nice candids can be taken during this group photo time. Use the Rollie for the ceremony and the 35mm for post ceremony and reception photos. 4 PM is a nice time outdoors if the weather cooperates. Look for controlled light, more horizontal, not overhead, use as your main light and a small flash as fill. Have your wife make photos of the ladies getting ready, objects of significance like the rings, flowers, shoes, purses, bride putting on makeup, groom and groomsmen getting ready, napkins, table stuff like silverware, place settings, name tags, items that will prvide memories for the b&g. Concentrate. You will be telling a story with your photographs. Get involved with each & every situation. Pay little or no attention to technicals as they should be down before the wedding. Go to the rehearsal. Check each venue before the wedding.
Maybe hire a pro & you offer to help!
I have found that being a guest, and a worker (even un-paid) at a wedding is very awkward at best, and puts you in a situation of losing a friendship at worst (if critical pictures don't work out).
It doesn't matter much that it is supposed to be a low-key affair.
That said, years ago, I vowed I'd never do it again, but guess what? I'll be doing a friends wedding next month. Do consider tellng your friend (nicely) to hire a pro, if you have any doubts.
But if you decide to press on, you have a good selection of gear, pick what you are most comfortable working with. Go to the rehersal, especially if you aren't familiar with the space.
Talk with whomever is officiating and find out how he/she feels about photos during the cermony, etc. Figure out where your best vantage points will be, so you aren't discovering everything fresh the day of the ceremony.
Thanks guys! I TRULY appreciate everyone's advice and concerns. I personally think I can do it. Can I do it as well as a pro who does it once a week? Likely not but I'll give it my best shot (pun intended). Looking at the weather, it looks like Sunday will be the only day that is going to absolutely suck over the next week, so outdoors may be a non-event. Wish me luck, I guess...and I'll be sure to post a few to get some opinions on how I fared.
My vote: F6 for ceremony or anything that's fast moving. Any of your medium format for portraits.
Happy to hear you're going to do the gig.
Relax, stay calm.
And have fun!
You will do just fine!
What a lucky couple to have you shooting! Not just a "grip-n'grin" shooter, that's for sure. Have a wonderful time!