IMHO the best place to ask your blog monetization questions are over here http://wordpress.ORG/support/
The most common ways touted for making money from blogging are Google Adwords, Affiliate Marketing, Google Adsense, Forex Trading Robots, Surveys and Product Reviews, Article Marketing and selling on ebay.
Well, the truth is no quick and easy way to make money online. Making money online or offline involves hard work. Moreover, very few bloggers have the degree of expertise required to produce content that brings in the massive number of hits on advertisements that are required to make a living from blogging.
How well do you blog now? How well does your blog do competing against the money making blogs in the here and now? Do you have a blog that attracts 1,000 - 1,500 unique visitors every day? If you don't then you will not make a significant income from blogging. You will be lucky if you make enough to cover hosting costs.
Will leaving wordpress.COM affect your blogs search engine ranking? Yes! Even if you buy domain mapping along with a domain the new domain will start with a PageRank of unranked and have to work it's way up from zero/10 again. Here's the catch 22.
If you are blogging for money then PageRank can be a major issue. Once your site has a higher PR (4 or 5) then higher paying writing opportunities become available to you. However, if you write for services like ReviewMe, Text Link Ads, Smorty, and/or PayPerPost, etc. then it’s important to understand that Google doesn’t like paid links, so if you have them and if your site doesn’t indicate them with “nofollow” or, if you’re active on the Internet selling links on your site then your site's PR will suffer.
If you don’t care about Google and PageRank then get involved with services like ReviewMe, Text Link Ads, Smorty, and/or PayPerPost, etc. and sell all the links you want. But if you don’t want to be harmed in Google PR updates then don’t sell links and don't link to sites that do.