Weddings and SPD, definitely a challenge.

For when he is Best Man versus just a groomsman, he might be able to wear something slightly different from the rest of the groomsmen. Due to this, once you find out which materials are the most comfortable for him, see if they can be tailored to be the majority of the comfortable material (especially the parts touching skin). If ties are a nightmare, see if the groom & bride will be OK with taking off the tie after the pictures and ceremony are over.

As a guest, then you can have a good suit tailored just for him of comfortable material. It costs more, but it is a much better option than freaking out mid-wedding because your skin is crawling or on fire.

At many of the weddings I have been to, shoes have been ditched or exchanged by many people (men and women) at the reception for comfort purposes.

On wedding food, depending on how bad your food allergies/intollerances are it changes whether you just bring your own food or ask for changes in the available wedding food to be safe.

On light sensitivity, this one can be rough in a wedding especially during the dancing time if there is a disco ball. Irlen Contacts are the only thing for me that make dancing when there is a disco ball possible. At my own wedding I made sure there was NO disco ball or dry ice.

On sound sensitivity, for my wedding I picked ALL the music (even the DJ's entire available list). At other people's weddings, if the music makes me violently inclined we leave the area where the dancing happens or leave the wedding early. I haven't tried earplugs, but it probably is a good idea to have them in a pocket so that you can pull them out when you need them.

On smell sensitivity, find out if the wedding is going to be in religious building that believes in a lot of incense. If so, just let the bride & groom know you can't make the ceremony, but you might be able to make the reception. If the problem is perfume and you can't breathe, congratulate the newly married couple and then go to where you can breathe. If you have to leave to stay breathing then you have to leave.

On touch sensitivity, if you do try to dance, find the most open section of the dance floor so that no one touches or hits you while you dance. If you are hyposensitive and crave touch, then go to the most crowded part of the dance floor and dance away. I personally need my own section of the floor or I quickly get hysterical or fall.

My own wedding that was completely tailored around my personal sensory needs was the most sensory comfortable wedding I have ever been at. My wedding dress and shoes were 100% hand made of only comfortable materials. Expensive ($1500) but worth every dime as I was never uncomfortable in it.