I agree with Roots 100%.
I think you should look at the RPG maker products.
Definitely start here. It's a tad costly (though you can find it on sale on Steam from time to time). You can also try GameMaker and Construct2, but RPG Maker is more RPG-focused, letting you get prototyping quickly.
As someone who has been working on a JRPG built from scratch for the last several years, I will tell you that it is a lot of work to build your own game.
Totally agree. While I haven't been doing it as long as Root's Hereos of Allocrost project, I've been working on my own RPG for 3 1/2 years now.
We use 32x32 pixel tiles, which seems to be more or less the most common size that games like this use. Our sprites are 32x64 pixels (2 tiles high), but if you're going for a more cartoonish or cute style, you may want to make them 48x32 or shorter.
My game uses 48x48, and character sprites are 48x96 (two-tiles high) - closer to 1 and 1/2 high. In-combat enemy sprites will vary greatly.
As a basic measurement in my own game, 1 pixel = 1 inch, so 48x48 = 4ft x 4ft.