Definitely do report any errors or bugs that happen. Firstly because this is a small community that needs this sort of feedback (I don't even mean opinions on balance/writing/whatever) to create polished and functional mods for the game. Also because you're quite likely to get small but critical fixes available within a couple days, or even hours if you're lucky.
Also, Knossos itself is still basically a beta if not alpha release, while lately its creator wasn't able to touch upon it due to real life matters, a couple community members were able to push some critical fixes exactly thanks to the people that used its functionality and reported bugs, instead of shrugging it off as "well, it's broken" and moving on. Feedback is really important, and you're very likely to get what you ask for, sooner or later.
Besides, people making the mods and tools really feel like someone cares when they get back feedback, and even more, some praise
. That gives them the strength and motivation to further develop their things.
Also people here are often looking for feedback from outside of the veteran Freespace community, simply because there are so many things that we take for granted and that new players have no idea about, which makes us run into becoming newbie unfriendly by default, that's why we need "fresh blood" and some insight from outside of our small corner of gaming.
As for campaigns, there is definitely a bunch of "famous" ones, BP, BtA, WoD, ST:R, Inferno and others that reached their position by being large, complex, with lots of new content... But the smaller mods are also very worthy of picking up too. Firstly because the people developing big fancy projects used to start small too, and you might as well be fueling some possible future mission design powerhouse with feedback, and secondly because even if they aren't complex or very fun, there's always still something noteworthy and unique in these. Also, if you want to know where to start, this topic has got some good suggestions: https://www.hard-light.net/forums/index.php?topic=80688.0