Ask HN: Advice on forum software

I am looking to create a niche community website (100 to 1000 users in the beginning) with a discussion forum. I had a look at some of the popular software (vBulletin/phpBB - also tried searching on forummatrix.org) but somehow I find most of them to be lacking in one way or the other. I hope HN community can help me if they have any personal experience with running forums. Here are some of my thoughts on what I am looking for (in the order of preference). 1. Good/Modern UI - What I found most surprising in my search is that most of the available software have a UI that is practically the same and it looks like all of them are stuck with their default UI for the last 7-8 years (if you are a regular on vBulletin-powered forums you would know what I mean). It is possible that there may be some custom themes that provide a UI that look stylish in which case I would like to know about them too. The closest I could find to my taste was Ning but I had to rule out Ning for other reasons (see point 2). 2. Hosting - F/OSS is desirable since I would like to know what goes on inside but I am not particular. However, I need to be able to host the site on hosting providers of my choice. This was the reason I ruled out Ning. Also, some time back I heard about Ning shutting down websites on flimsy grounds, so I prefer to have some measure of control. 3. Chat - I hope to have a lot of private messaging between users so an unobtrusive chat plugin would be desirable (like the Chat feature in Gmail). It should support group chat(multi-user). 4. Social networking - Profiles/friend-ing(for lack of a better word)/photos/likes etc. would be nice purely in the interest of building relationships between users but it is not a core feature. Voting on stories/topics ala HN is not necessary. 5. Tech support - I should be able to jump in and resolve most technical issues but I would rather focus on managing/growing the community, so I would like to see some decent support for troubleshooting issues. Even if you do not know specifically about the software, I would appreciate if you can point me to some well-designed forum sites that you personally like.