In my current project (not an RPG per se, but a game that handles stats in much the same way) I use a bit of everything: Base stats are stored in local variables; upgrades to those stats are stored in arrays; anything that I need global access to even when the player isn't in the layout (in your case, stats like XP or gold) are stored as global variables.
There's no universal wrong way or right way to store the information that you need - it just depends on the situation. I'd suggest that you start off with what you know. Arrays seemed like a weird, foreign concept to me when I started with Construct two months ago, and now I'm loving how useful they are. As my project has progressed and become more complex, I've grown to use the tools available and find better ways to manage things in my game, and I'll continue to develop new skills. I'm sure you can do the same, too.