You have to get visitors to your site in order to get members, so your initial focus should be on that.
Before opening an online dating service, it's vital to have a strategic initiative in place. This means at least a Web Marketing Plan and Business Plan. A Strategic Traffic Building Plan wouldn't hurt either. You also need to have a Web marketing or search engine optimization expert on board. But positioning your site in the highly competitive online dating terms will not be easy. Yet most people still find sites via search engines. If you don't know of an expert, come up with a way to barter services.
Chemistry.com was very smart in their launch. They first targetted specific cities. It's much easier to first build a user base by focusing on 1-3 cities than it is to first focus on the world.
I made some other suggestions in this post.
Online dating is one of the most competitive markets online. The serious services launch with marketing budgets in the millions. This automatically puts smaller services at an extreme disadvantage. You must have tenacity, ambition, drive, and strategies to succeed. And you also must be willing to lose a lot of money initially - particularly in the first year. It's not easy to break into this marketplace. Around 99% of new services fail. You must plan to be an exception to that rule.
Good luck to you,
Joe Tracy, Publisher
Online Dating Magazine
Online Dating Industry Journal
Columnist, Inside the Online Dating Industry