Working on an Action RPG myself. Different beasts in a some ways, but other ways they're similar. Might be easier to do a turnbased jRPG though.
1. Construct 2 can pull it off perfectly fine. Lots and lots of ways to do it, you just gotta find the implementation that works best for you. My tip would be get really familiar with arrays and object oriented approaches. That way you can minimize code but keep your engine flexible enough to add enemies, items, equipment, characters, etc... Everything can be accomplished in events for sure.
2. The product is geared towards anything you want, really. Action/platformers are just easier to pull off in a lot of ways. Most of the action games people make with it have very little if any RPG elements at all, because RPGs are a ton of work. That said, you'll find challenges either route you take. But it can pull off both just fine.
3. Using layouts for each map would be less system intensive. That said, depending upon how you optimize your game and how you setup your mechanics... the way you go about it doesn't really matter. What matters is the end result, what the player's experience will be.
Welcome to the community!