My photography forum used to be pretty busy, but it's going to be replaced by a custom site... when I get round to it.
The funny thing is I thought running a photography community would be fairly easy, but it proved to be the most challenging - it's very difficult for people to take (and sometimes give) criticism of work.
I would just google photography forum and read a few - the culture will be quite different on them, some will be more welcoming of newbies than others..
I use DPR pretty much daily and I've always wondered what forum script they were using. I think the way they display EXIF data on mouse overs, etc. for pics (since the site is photo centric) is (or maybe was) unique and apropos.
However, I could not find info re: 'bespoke forum software' that you mentioned above. Do you have a link?
It's not a common word in America. Most people don't know what it means. Tell someone you purchased a pair of bespoke brogues from Foster and Son and they'll look at you as if you just grew a third eye. Tell them you had custom, hand-made shoes made for you they'll understand. At which point they'll think you're insane for having spent about 2800 quid for a pair of dress shoes. They last for ages.
Custom; custom tailored; tailored; unique; etc., would be more common words the average American would understand.