A while back, a certain adult company had some cousins that decided to start a non-adult subscription web site. Noone had any expertise in the 'hobby' other than the fact that the niche (neesh, nich, neeshay

), was one full of rich (reesh, rich, riishay

) people with lots of disposable income. Aside from no experience in the niche

, none of them particularly liked the niche

, and about 8 months later the site was shuttered temporarily. Seems that along with not liking the site, paying for hosting was also not something they liked. So, the server was moved from one place to another, shut down again, later moved again. The site is still up, but I would doubt there is much revenue being made.
So, I would advocate someone going into a niche that one enjoys or likes so that it is less painful drudgery when actually having to work. And work is also a key ingredient. Unlike years ago, it is much more difficult to make it in adult without putting in some effort. If you're afraid of work, getting rich is going to be a tad more difficult.
Spend time crusing the boards and doing personal networking. Learn the players, learn the tricks of the trade, talk to people and get to know them. When someone shares a mutual respect, working with them, traffic trading, etc. is a little easier.
Choose sponsors that are reputable and willing to work with you. You're not going to find too many sponsors now days that will handhold you, but, you will find plenty of community support out there while you are learning the ropes. And they will point you in the direction of decent sponsors. Boards like this one have a great resource list
http://www.greenguysboard.com/resources/ to start with.
Basically, everything you do in the business is like a partnership. Choose the wrong partners, and you make no money.
Oh, and be sure to budget $5k for a really cool sig tool

I hear its all the rage.