So, I can completely empathize with your idea and I’m not trying to dissuade you from it.
But, like someone else sort of mentioned, building the app is really only a small part of the question you are asking. Almost nothing.
Getting and retaining users, and then getting those users to pay you or attracting a sufficient number of users that makes Adsense/etc worth it… That’s really hard. And it’s a totally different ball game than simply coding an app, even if it’s good and beautiful and useful.
I think a good resource for you might be www.indiehackers.com or maybe searching out a community of other developers doing this.
I’d also say that rather than thinking about having this huge webapp that tons of people use and investors care about, start small and use staggered goals. Cover the site’s hosting by getting it to $10/month, say. Then $50, $100, and so on. Practice ‘just in time’ development (i.e. worry about load balancing when you have enough traffic to care about it; make something people are already asking for; etc).
I’m sure you can get something simple earning at least a few bucks. That’s an interesting project in its own but to hit on and execute an idea that would replace your job would be quite difficult (but not impossible!)
At the same time, realize there are people out there making $1000s a month from having the most popular word counter/egg timer/crossword maker/etc online. It can be done and it doesn’t require a huge messy app to get there. Good luck!