I think you need to ask yourself basically what you are trying to achieve:
(a) Do you want to create a whole new type of niche magazine that shakes the magazine publishing industry to the core?
(b) Do you want to create a magazine that is financially viable but one's whose subject matter is wholly exclusive which is what niche is about?
(c) Are you sure people want to read this magazine you are creating?
I think these questions are extremely important to ask yourself before you commit to making that journey into magazine publishing.
I am not sure what market you are aiming for regarding niche magazines but I think if you hope to create a financially viable magazine, think outside the box and try to find content that will appeal to the target market that has disposable income to spend on magazines.
Most of the money you will make, especially from a niche magazines, will 100% be through subscriptions. So the magazine has to be something that is offering not only content to the reader, but an experience.
Think about the magazines you like -- why do you like them? Do you like them because they are original and fresh? What features you like?
I think you could set yourself a few tasks to figure out if your idea will work. Do some market research and find out what people think is missing.
The Internet will not kill long-form journalism, which mags like the Atlantic have perfected but what it will do is destroy breaking news in magazines. So whatever you are aiming for, make it stand out from what the Internet offers and give your potential readers a great experience.
Advertisers will want to see a beautiful magazine but they want a magazine that will speak to their target market. Say your magazine is about finance in the Caribbean, you will thus need to convince advertisers that you have a glossy clientele of readers who have money to burn in the West Indies as they do their business there. You will need to create a profile of your clientele because that is what your readers are -- your clients and you must treat them as such.
Here are some links that may help you on your journey
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MediaGuardian -- This is the media supplement of The Guardian Newspaper in the UK.
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Magazine Launch -- It is not updated frequently but the forum's archives are a goldmine of information and help. I have posted there before to help people.
If you can get some work experience at a magazine too, that will also help you to see how an office is run unless you have done it before.
Let me know how it goes for you.
Cheers,
Aulelia