If you visit the websites of some of the guilds you can get a good idea of how they are organized and what they offer members. Some are very large, others are quite small. They are usually started by a small group of people who want to establish an organization to promote calligraphy in their community, offer educational opportunities, and have regular meetings for scribes to get together. Most groups meet monthly and have a topic presented at each meeting. There is usually time for people to share the projects they have been working on.
Many years ago it was more difficult to find ways to publicize the organization. Today, with all the social media options it is a lot easier to get the word out. It is good to network with the art supply stores where calligraphers are buying their supplies. Some of them have class rooms that are available for meetings. Many guilds like to meet in libraries because they publicize the groups that are using their meeting rooms. Finding a place to meet can be challenging. It is nice to be centrally located in a community. The day and time is also challenging as there are people who can never attend on the weekends and others who can only attend on weekends. Meetings tend to be for two hours.
Years ago, most guilds published newsletters. Today, information is usually posted on a website. Blogspot is a good option for a free website.
Dues. Most guilds have a membership fee. You might wait on collecting membership dues until you have enough people to make it worthwhile and have figured out why your organization needs a bank account. Large guilds use money for things like exhibits and community outreach or to subsidize the cost of bringing in rock star instructors for workshops.
Most guilds need several members who are teachers as the main focus of most guilds is education. If you do not have several people who teach who are interested in starting a guild, you might consider calling it a club. Medieval guilds were more like a professional organization for craftsmen. Modern day calligraphy guilds are made up of both professionals and hobbyists so they are more like a club. There is a lot of variation in how guilds are run. If you can find a group of people interested in a guild you probably need a lot of input from the people about what they feel would make it worth their time to participate.
The hardest part of managing a guild is finding enough people to volunteer their time to keep it running. It's not that hard to find people who want to join a club or guild to network and learn. But, if there are only a few people doing all the work of organizing, booking the meeting rooms, planning the programs, publicizing, running the website or blog, etc - those people quickly burn out.
I am happy to answer any additional questions. Guilds are wonderful organizations and it's always a good thing to get one started. If you check the list of guilds - and visit their websites - I am sure you will get a good idea of how varied they are.