only a small number will sign up for a specific forum

Most people don't have to sign-up, 90% of cases should resolve on just searching the problem. Good chances it was already asked and answered.
Most of the time, forums with few users aren't dead, they're just really slow, whenever you post a question - expect at least 12-hour delay. I've never seen a message on Discord answered 12 hours later - you either get somewhat instant response or it's ghosted forever. Also good luck asking questions if there's heated/rapid discussion in the room, or you have a little time and other responsibilities other than checking discord every couple minutes.