Hi there, welcome to the forum! Your overworld's looking pretty sweet.
If you're not sure what to do (or what you CAN do),
you might find this guide helpful. It's a step by step tutorial for making a fantasy rpg called the Ring of Udrai, and it's designed as a teaching tool for beginners, so as you make the game you learn what you can do and how to do it. I followed it when I was first starting out and it was the best tutorial I found for learning the programme.
It's written for RPG Maker VX Ace, the version before MV, so some stuff will be outdated or missing (for instance there are now two kinds of battles, side-on and front-on, whereas in VX there was only front-on unless you used plug-ins). But things like building maps, scripting events, scripting monsters/bosses and so on seems to be the same, so I think it'd still be helpful.
Good luck with your RPG :)