Boy do I miss this kind of RPG! I'm getting some strong Dragon Quest 1 vibes, which I adore. It's simple and effective, very well executed, the graphics are great and very cohesive. Some music is from Dragon Quest I think, the town music doesn't quite fit with the rest, but that's all I have to say about the presentation.
I've played up to the point where you get the boat, I intend to complete the demo later.
The enemy strength curve is great, to me it's the hardest thing to get right when you program an RPG. I think you've got it right. That said, while spells that inflict a fixed number of damage are really useful for a little while, they get pretty much useless for the rest of the game. I think your fireball spell should have varying damage, or at least it could be automatically upgraded at some point when you level up so it doesn't take space uselessly in your spells lists.
When you equip an item on an empty slot, I wouldn't display "you have placed nothing in bag" but in a way that message feels retro :)
Being able to autobattle would be nice to speed up grinding and exploration, it wouldn't be out of place as thew old Phantasy Star games allowed that if I remember correctly.
I can't say miss the good old "inventory full, sorry!" when you pick up an item, but that's part of the fun I guess :D It's nice you implemented that too.
Finally when you buy or sell, instead of closing the menu, it would be nice for it to remain open. For instance if you buy an herb, that would take you back to Buy/Sell.
Great work, keep going!
PS: If you could make a build for Linux and Mac, that'd be cool!