Hm, just for the experience, I'd be interested how it works out, so I'm saying yes to an experiment with ads.
Some personal experience with ads:
I've been the admin of a free forum for 3 years now. The only reason it can be free is because of the google-ads that occur on all pages that are shown. It's the consequence of using that free forum service.
I have no control over the content, frequency, size, placement etc. of those ads at all, also the consequence of choosing that free forum-hoster. If I'd want control over ads, or eventually remove them, I'd have to either buy a contract with that same service so I can continue to use the same url and forum data, or move to another hosting service and set up my own forum there and start over from scratch (I wouldn't like to throw that away, 60000+ messages and 700+ users )
But I'd need paying/donating customers (members) to be able to pay for the hosting, and because it's a mostly 'more mature female audience' (subject is machine embroidery, Dutch language only, the estimated average age is well over 50), and it's been free from the beginning, that would probably cost me over 80 percent of the current users, so that's not an option I'd want to even consider. And I'd be forced to either close that forum down, or introduce ads to pay for it...
The current ads are on the top and bottom of every page, usually pretty on-topic with the forum-content. Hey, as a 'regular visitor' I even get google-ads with that kind of content on other sites that use google-ads