Honestly, all the topics you listed are either saturated, or not highly discussed.
Quote:1. Gaming
2. Coding
3. Social Engineering
4. Computing and diagnosis
5. And General(jokes , funny stuff etc)
1. Gaming is so overused it is not even funny. You will not be able to compete with the forums that have been around for years already. Might as well drop it (I would) in a business standpoint.
2. Quite a hard one to start with. You'll have barely any traffic because the audience isn't quite big. There are a lot of people who are interested in coding, but they're probably already on another forum, like CodeGuru, Dreamincode, etc.
3. This was a very popular niche last year, and I think has started to die down with the calming of Social Engineering methods and support from people who are actually into that.
4. Could work, there's forums already, but it's not quite overused, like Gaming. I don't know anything about making a forum on this topic, so I can't help you much in this one.
5. That niche will never, ever work. It's too broad. People who join forums want something specific, like an Android Phone forum, is for phones based on Android OS, it's quite specific, but broad enough for users to join and share information on other phones based on that operating system. I'm kind of going out on my own in thought, but that's just how I am
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You should invest in a cheap VPS. It's great to learn on, running a forum on it shouldn't be much work, besides installing some daemons, security measures, etc. Free Hosts are a big no-no. Anyone can get on the host and do what they wish, i.e., finding exploits, and if they're on the same box as you, oh you're not going to be happy. Don't forget performance issues. You're better off with paid shared hosting, or a VPS for dedicated hosting.
Now, to think of a niche, you just gotta do some research. What are people interested in the most, but that's not too available? You can compete with forums that are semi-large, or even large. It's just all about what your forum can offer people that the competitors don't, and what people want that the competitors don't have. Just think, man. It'll take time, but don't jump into a forum if you have no research taken in a niche that you might want to use.