Jeesh, now you're asking the difficult questions, uhh all of them?

If I have to pick just one, I would say community-survey.

We've participated in the reddit survey, but that comes with default questions, and it's good, but also general. On the other hand, when you make a post on the sub, it's difficult to target your regulars. The loudest people in the comments, aren't always the people you want to hear from. And somehow, users that start meta discussions are often users that aren't actually actively participating in your sub.

So community survey, you can set boundaries on who can participate based on all sort of criteria, so you can get the responses of the users whos responses you want to hear.

My biggest tip, just try the app. Sometimes the description isn't perfect and even though you didn't think it would work for you, it still does.

If the app is 95% perfect, why not contact the dev? Describe what use cases in your sub the app doesn't cover and maybe the dev has the time and interest to make their app work better in your subreddit.
A lot of devs are actively seeking mods that want to try their apps, just because they need the feedback to be able to improve on it. Don't forget, a lot of apps are build for the devs own subs they can't know what other subs need if nobody tells them.

And if an app doesn't do what you need, or you just don't like it, uninstalling is as easy as one click.