It comes down to conversion rate, the CPC you earn as an affiliate is roughly the same as you could earn from an ad network (affiliate marketers doing price arbitrage ensures this is the case).

But if you can produce a significantly higher conversion rate by integrating the affiliate links into your core product then it may be able to generate you more income.

You can get the affiliate payment rates fairly easily from someone like Amazon of an affiliate network like CJ so use them to make a spreadsheet and figure out the kind of traffic and conversion rates you'd need to make a viable startup.

Yes, but only if you have millions of unique visitors a month, and the niche is ludicrous like health/weight loss, personal finance, investing, insurance, etc. Once you gain traction, you can skip the middleman and go directly to the business, like Mint.com, Bankaholic, and InsuranceAgents.com.

If you're trying to sell low margin items like books, and even electronics, it's not sustainable at all. Not even close. Just do back of napkin math and you'll see...

Consider the alternatives; try to go direct to the brand names. If you take a look at the music videos by Black Eye Peas or Lady Gaga, that's a few seconds on various products; watch, etc.

In whatever apps you are building, consider who uses it and what is most inline to advertise, do direct to them. The return is definitely more than what affiliate links will bring you.

Can it be monetized this way? Yes. For your specific idea and the way its implemented, depends. Too vague to give any tangible advice but if you are just asking if affiliate income works for other models, then absolutely. I can validate that much from experience.