niche question

hello dear bhw members
ok i was fooling around on google keyword tool
just searching for my passionate niches
i found a niche that have over 2m from usa, 1m from uk and totally 10m worldwide search with low competition ( which means in google keyword tool that there is not a lot of people who bid on it, in simpler way people don't pay much/ and a lot to put their ads on that niche)
however it have another keyword that have medium competition but around 100k or so.
so i went to check the google and see how many people have websites on that niche'
i found around 120k websites, 92% rank 1 and 0.
so with my bhw knowledge i have the opportunity to make on first page within 1 month using BH, but around 65 days using WH depends on google indexing really (last one i prefer so it could bring steady outcome for next 5 years or so )

so what u guys think?

after searching and monitring for 3 hours the top ranked facebook pages, forums and some websites.
i decided to go for it
my bet: huge traffic will counter the low paying ads
test phase: 1 month which needed to have 100 unique visitors everyday, and 150 $ in the end of the month ( that is for all month, not everyday)
or will drop it'
work hours per week: 20-30 hours

If by rank you mean toolbar pagerank then you should know that it's definitely not a proper way to determine competition in the serps. You should definitely also be looking at the amount of backlinks, the quality of those backlinks, domain age, and other factors to properly determine the competition. Ideally you'd want to hit the first page in the search results, which makes the websites currently in the top 10 your competition and therefore you shouldn't worry about the 100k+ other sites. But you should try looking a few pages back aswell, as I do believe that these pages are also pretty profitable for a niche with high volumes of searches.
Also to my knowledge there is no way to determine how long it'll take to rank beforehand no matter what method you're using.
At last, I'd like to remind you that just because you're building backlinks by hand doesn't make it whitehat at all. Any attempts to manipulate the serps is blackhat. White hat is writing articles, on-page seo, and praying everyday that someone is going to discover your website in some crazy way, and is actually going to like your content enough to share it.