Build something awesome.
You need one of two things to get a large payday - customers who will pay for it, or a shit-ton of traffic. To acheive either of those, you need to build something great. Focus on that - if you need to make money in the near term, beg/borrow/take investment or get your customers to pay for it. Any other route will impede your advancement. In fact, shopping for investors can impede advancement just as well.
Getting money from your customers is the only path most startups should focus on. If your customers won't pay for it, it may not be worth what you think.
Save the ad model until you have a ton of traffic. If you try to monetize small amounts of traffic in this way, you may never get to big amounts of traffic.
So I guess my advice boils down to 1) get customers to pay for it 2) if you can afford the infrastructure, just focus on growth until your options open up or traffic hits a point that you can monetize.
But I guess I should have started all of this by asking - what's your business model? Is it something people will subscribe to? If so - perfect - there's your answer. If not, is your audience either large/in-demand enough to warrant ad revenue? If not, you'll spin your wheels setting up your ad spots, likely screw up the user experience and gain a few bucks a day. I think your idea/product probably already has a natural fit for which way to go, try to find it.
Just my opinions of course.
Advertising - Much, much harder than most people assume, requires scale, and low traffic costs. An add network like adsense is by far easiest but most startups find the CPM (cost per 1000 impressions) rates they get via selling ads themselves or using a specialized ad network are 5-10 higher.
Sell a service - For most startups in the web 2.0 world the "freemium" model works well, where you give something away and upsell services on top of it.
Lead Generation - Generate and sell business leads.