Narrow down the topics by reflecting on profitability and other goals. In order to make money, you'll need to find a niche that other people haven't filled already, but is still popular enough to attract a significant number of visitors. Also consider other factors, such as money you'd have to spend if your blog focused on reviewing products that you in turn would have to buy.
PS: my answer to this question is always… “the better question is… how can my blog help me build a profitable business?” Most of the profits from blogging are not made on your blog, but that’s okay. I don’t believe blogging about making money per se, but about branding yourself and positioning yourself within your niche market as an authority and leader. Once that is established, there are so many ways to move people into your money making enterprises. Email marketing, as you pointed out, is one of the best ways to do this. Sending people to your membership sites, services, info products and coaching programs are all great things to route people into as well.
Consider affiliate programs. By finding an affiliate program suitable for your blog, you agree to provide links to a company's products, and in return are paid for each reader who makes a purchase after following your link. You can find specific companies by searching an affiliate directory such as ClickBank, or by searching individual company websites for affiliate programs. Consider these factors before you choose an affiliate program:
If you’re passionate about something, it will show in your content. Readers will be able to see your genuineness and will be attracted to that. This is probably the most important thing you will learn about blogging. You can try everything in the world and use every tool known to man to be successful, but if you’re not genuine, people will see right through it.