I will make one more set of observations about wedding photography, but NOT brand or gear specific. There are often cases where people are asked to take on a role as photographer at a wedding or similar event: either because they are friends with the wedding party, or are aspiring to start their own business and are looking for gigs.
When one puts oneself in the position of doing what a professional would normally do and charge for, especially as the sole provider, they are essentially acting in that role with those responsibilities and expectations. It is critical for them to understand that at weddings in particular, it absolutely important that they do not let down the wedding party by not delivering the quality of the images expected, negotiated and agreed upon. Often people will expect top-drawer images in ignorance of what that actually entails in terms of gear, skill level and resourcing (including multiple shooters), so it is important to define expectations and align them with capabilities; and if one cannot deliver, don't do it. A wedding is a highly emotive event and will hopefully be a once-in-a-lifetime one, so no failures are acceptable. NEVER EVER OVER-PROMISE AND UNDER-DELIVER!!
In terms of gear: one needs to have duplication of almost everything - dual cameras, with dual card slots in case of gear failure, multiple batteries and cards etc. Especially if one is charging, that tends to push the quality towards the higher-end FF units such as the R1, R3, R5 and R6 units. Those are not cheap - one could have a mixture: main camera being an R5 variant with an R6 variant for backup and with different lenses attached. Yep, one does not have a lot of time to change optics, so planning ahead to know what lenses will work for each stage is critical - as is knowing the characteristics of the venue.
Is it dark, light, do they allow lighting or not, so serious recon is critical. What about outside shooting? Midday in a cloudless summer day is a terrible place to put people in the open: they squint, and have shadows in their eye sockets, so finding attractive shaded areas to reduce contrast and dynamic range is important. As is having a wet weather fallback - people don't like getting drenched in wedding attire.
If the expectation is to have video as well, then a second or third shooter is advisable. Video is its own skill and demands total attention while shooting, and the videographer will want to shoot from different but simultaneous locations to the stills photographer.
What will be produced? Is the responsibility to generate image files for the client to use as they please, or are they going to want anything from a few modest prints to the whole gamut of books, large prints in frames and videos with post production and commentary. Is that within the capability of the photographer and do they budget for it? Those things need to be confirmed and agreed upon, as is the delivery timeline. For professionals all this should be fairly obvious but for newbies or socially engaged amateurs it can be a minefield with the potential for ended friendships. Also, don't forget insurance for your gear or personal injury.
Technique: As simple a thing as how to hold a camera for stills photography: in the main one should always shoot via the viewfinder when going hand-held. Tripods have three legs for stability, so the photographer needs 3 points of support: viewfinder to the eye, left hand under the camera and lens with the heel of that hand under the body. That leaves the right hand to lightly manipulate the controls. The other two points of contact are by tucking the elbows tight to the sides of the torso. Don't rely on image stabilization, use the right technique, and it's also better for the photographer's posture and back.
Other stuff:
Interference: everyone will want to bring their cell phone and record the wedding. They are a bane to the photographer as they get in the way. If the results are to be delivered, there must be an understanding between those organizing the wedding and the guests that the photographer takes the photos. This can be done diplomatically but firmly by the wedding party.
Speaking of diplomacy... emotions run high at weddings, so the photographer is wise to inquire about any potential issues - split parents refusing to be in the same photo with each other, dominant guests who will want to organize the photographer, unruly guests. Those who hate having their photo taken.
Security: The photographer is likely to have quite a bit of gear, given all I said, so they need a secure but accessible place to put it so that guests don't get a chance to play with it.
Catering... weddings and the post nuptials will go on for hours, so the photographer needs time, water and food to be able to not collapse. This needs to be confirmed and a good time to eat agreed upon because they won't be doing any photography. Such things as venue parking need to be agreed as well.
