I think my goals are not overly ambitious: I plan on doing this for the next 4 years as a hobby while I'm still in college and if at the end of these 4 years my website(s) could make me a few hundred dollars/ month that would be a great first goal for me to get started in the world of internet marketing (I know it cant be taken for granted, but its my first goal!:-)).

I'm wondering how to tell if a field has enough potential and what Im having an EXTREMELY hard time with is this:

I'm trying to have an indicator to be able to tell if there's any potential in the field or if it's too "niche".

I usually look at the keyword with the highest search volume, look where in the SERPs I could stand a chance to rank for it (by analyzing competitors IBLs and keeping click through rates in mind..just to get an extremely rough idea).

But what I'm REALLY struggling with is this: The highest volume keyword will probably be my main keyword for the homepage (from where Ill break the site down into sub-sections).

However how many % of the organic referrals should I expect to enter at the homepage/how many of them can I expect to be referred from the #1 keyword?

For my goals that I described above - how high should the volume of the most generic/highest volume keyword that I'm going for be? If I can make a huge website on that topic would it be enough if I can expect to get a few 100 searchers from my highest volume keyword as that'll mean I could get a few thousands of visitors from all my SEO keywords?

THANKS!