I'm going to be doing a similar writeup as my app launches in 2 weeks. I've got a small budget. All the design+dev was me, but I'm spending about $300-$400 on marketing. We'll see how that goes.

If anything I believe you should be spending more on marketing nowadays. There's no real way, at least to my knowledge, to search for a niche hole with keywords. I do, however, like to think of an app idea and then spend an hour search various keywords and seeing the results/competition. https://appstorerankings.net/ is a good website to find the keywords of an app. I combined common keywords in the app that I'm releasing with common keywords that are missing among competitors that yield few results.

Again, I haven't launched this app (my 7th) yet, but I'll be doing some analysis of its success using the marketing budget and keyword research.

I agree it's hard to do really detailed research similar to, say, the Google Keyword Tool. It's mostly a gut check. "Does this have a lot of competition? Does this keyword appear to get a lot of searches?"

What's your app name?

Poetreat. Aiming for May 7. Week of polish then submission. http://poetreatapp.com/

Nice landing page for sure. Maybe this is obvious, but they key is finding out a solid upgrade that makes IAP's worth it to customers.

Agreed. Doing a freemium model where you can save only save 1 poem. Unlocking adds theming, Facebook+Twitter connection, and unlimited poems. Worth $.99? That's subjective, but this entire app is more of an experiment than a business. Just going to iterate and improve on the next one.

Nice landing page.

Thank you :)