I don't know anything about that group, but my suggestion is that you visit a couple of meetings and maybe an open house or two. We were very active in the Denver Garden Railway Society when we live there. The clubs that I have had contact with welcome beginners and are a great source of information about running trains outdoors in the local region.
Most groups welcome visitors and after giving them a look see, you can make an informed decision about joining or not.
Welcome to the world of "G" gauge in the garden, or any other place. I've been in this part of the hobby since 1980 and this past winter I got my first live steamer.
Chuck has some great idea.
They have a web site you can read up on their activities, copies of newsletters, slate of officers you could contact, a link to Join downloadable form etc. The $20/year membership seem reasonable.
There are a lot of mistakes that I made thirty plus years ago when I built my first garden railroad. Joining a local club and asking questions as you build your empire will help avoid many of the common mistakes. For instance, if you lived in a desert environment you could leave wooden buildings out, but in the wet east it isn't that great of an idea.
We have a number of wooden buildings, but they only go out for special times and never in the rain.
Because I didn't have any problems with water, drainage, on my Colorado layout, I didn't worry about it when I build my present layout in Virginia. Bad mistake. After every heavy rain my track is covered with debris from slope wash.
The mantra I give to beginners, don't repete our old mistakes, come up with a new one!
A better question might be...why wouldn't you join?
As membership chairman of a another GR society I can tell you that we appreciate all of our members regardless of their experience or ability to attend meetings/events. Even if you only attend one meeting or event a year, I think you will only find benefits in being there. In addition, your annual dues (which are usually minimal) can really help out a club to cover their expenses.