Action-adventure game for mobile is exactly what I've been working on for the past 2 years.
My last 2 projects were exactly in this genre, mobile action-adventure FPS. They were inspired by Unturned.
I would like to discuss further about the kind of mobile adventure game you want to make, and its scope. Being such a fan of adventure games myself, I'd love to offer you advice and support with your idea as well, if you need it.
As for my experience, I've been doing mobile game development since I was a kid, and full time professionally for about 3 years now. My biggest mobile hits are adventure-survival FPS games. The Outlands & The Outlands 2 (over 100k downloads for both, on android and IOS separately) might be very similar to the project you have in mind, there probably are many mechanics in these projects of mine that you'd like to see in your too. Even if they aren't, there's no problem, I'll design them to your liking.
I'd like to hear back from you, about your project and its scope, and also about its monetization. Is this a free to play game monetized with ads? or is it a premium app? This info will help me design a framework that would facilitate the implementation of your preferred monetization.