Maha Sarakham, is a pleasant quiet town about 65km South East of KK. It has a newish University campus and is probably well stocked with suitable chaperones for you.
Sounds as if the wedding, or maybe reception has booked a hotel, who are more upmarket than the average and they may well have a table plan. There is quite a bit of variety in the course of events, but typically the couple may invite 9 monks and relatives to attend a blessing that is often early in the day, from 7am onwards. That is normally followed a little while later, or maybe a lot later, by the wedding which is conducted by a senior figure from the community.
None of this recognised by the law as a legal marriage, that is a normally private quick paperwork excercise at the amphur office, not usually the same day. However the Bhuddist wedding is what most of the community is reffering to as getting married. The ceremonies followed by eating drinking singing and some dancing etc.
Forgive me if this is over the top info, but you did say never been.
Also some guys may say this not to do with biking, and may belong over on Thai Visa etc, but hey we do live here and its as good an excuse to get away on the bike as any.
Not sure how this is going to get you into Laos. You can travel East from Maha Sarakham but it is about 200Km to Mukdahan and a border crossing, or you can go North to Nong Khai, thats about 240km from MS,
but there are issues crossing over the friendship bridges into Laos with motorbikes from Thailand. No issues going the other way, Laos into Thailand, so maybe you want to cross the river somewhere up North, then travel down thro Laos and back into Thailand at Nong Khai or further down at Mukdahan, then on to the wedding. I have no experience to date crossing into Laos and cannot comment, but there is loads of good info on this forum on the subject.