Would starting out using let's say Xenforo when making a forum be a good or bad idea? When do you know when you should switch to paid software, if ever? Do you think people are more likely to join a site that is using paid vs free software, such as MyBB?
I really like Xenforo from what I've seen of forums that use it, but is it worth the price? Is it easier to customize? And how good is Xenforo's built in seo?
Paid forums attract more members but I don't think it's a wise idea to start off with paid software. Who knows, your forum might not do really well and it'll be such a waste. As least with free forums (most of them do really well, in fact) you can convert easily to a paid software if you forum is successful. Paid means are really expensive too, so maybe you can take the time to save up for it whilst you're using free software.
I was also thinking of the same thing, but I decided to start with free phpbb, I think if the forum does grow, change than otherwise you would end of losing lots of money. And surely people will like change as you do tend to get bored of the same theme and design after a while.
I think paid forum software might attract a slight amount of people but what it truly boils down to is how you've customized your forum and what kind of content you have on it. There are plenty of forums that are run on free forum software like MyBB that are HUGE, simply because the content is good while their theme and appearance looks very outdated. Hell, I've even seen a forum with over a million posts that still had the default theme and logo. Content is king.
That being said, I think it would be better to just start out with a free forum software to see how you do, unless of course you 1. have the money to invest in a paid software, 2. don't mind risking losing it.
I'm somewhat biased because I'm a MyBB fan but to be honest, I've enjoyed using MyBB just as much as I've enjoyed using IP.Board which is my all time favorite forum software. MyBB is very easy to customize and work with which is honestly a big factor of me liking it so much.
All in all, if you have the money to do it and don't feel like failing will harm your wallet, go for it.