The first two would both be good choices. The difference between them
is the broadness or narrowness of the niche. The first one is a broader
niche, which means it will take longer to hit the top 2 pages for your
site concept keyword. A narrower niche can go up faster.
However, the broader niche has more demand, so long term, it is likely
to be more profitable. It may have more ways to monetize too.
The are two other things that are important in choosing your niche.
Which one is more exciting to you? To write from 100-200 pages, you
need to be very interested in the topic, otherwise it will become a chore.
The other thing is the secondary keywords. When you look at your brainstorm it numbers, you can press on the demand column. That will move the kekywords so that everything is in order of demand from highest to lowest.
Your site concept would be the highest, as the seed word. The keywords
below that should have at least 10 words or phrases with demand of
around 1000 or more. They should be words you can use for your T2 or navigation bar sections. Then the lower ones should have a bunch at 100 or higher for your T3 pages. Do they look like they would make good sections?
Can you visualize which Navigation bar they would go under?
The third one has more supply than demand. That means more people have
information out there than there are people searching for that information.
Those are sometimes very profitable, but to beat the other 56,000 sites
will take a while. The general thought is to look for a minimum profitability
of 1000, but it's not set in stone.
Hope this helps.
Kathy
P.S. Congratulations & Welcome