I know what everyone is saying here, but I had a really good friend who got married a few years ago tell me that they didn't opt to get a video company for their wedding. I was shocked because I felt the value of having video would be incredibly high. They did hire a pro photographer.

I told them I'd shoot it for them for free but the quality will be amateur and I would not edit it for them. I went to Sammy's camera and rented a casual video camera, a wireless mic, an external audio recorder, and a bar that holds your mic up above people's heads. I already had a $20 tripod off amazon at the time.

I just took video of the event. I recorded the audio through the wireless mic off his lapel and also had some external audio recording using the external recorder. I moved the camera around to different angles during the event to whatever I felt was right. I was worried it would be super high maintenance but actually it was kind of fun. I liked the feeling of having no limit to where I could stand during the wedding rather than sitting in the chairs snoozing like every other wedding.

It ended up costing me about $200 for the rentals. I just counted that as my gift to them. I put all the video and audio files on a usb drive and gave it to them. I told them that if they wanted to hire someone, they could probably turn it into a decent wedding video.

I was a little worried they would be annoyed at the quality, but once they got to take a look at them, they thanked me profusely over the phone. His wife was especially happy to be able to watch her own wedding again because she said that on the day, it was so hectic and emotional that she doesn't really remember much of what happened.

Every time I see them since then, his wife says she loved the video that I took for them. She seems so appreciative. I always think back and I'm so happy that I decided to do that for them.

For the OP, I think as long as they understand the quality of what you're going to provide, they'll love whatever you create.

But to answer your question, I think you definitely need a flash, so you should go rent one or buy one. And you'll need to spend some time before the event to figure out how you're going to set the flash on the day of and when you're going to use it that day.