It's mostly Visual Balance and making the IMPORTANT stuff prominent. Whats the hierarchy of information? When the player opens the menu what are they looking for?
Hit Points and LV. will probably be at the top of the list, so Big and Bold
Money, depending on it's role.
It's not a bad idea to use separate typefaces, but it needs to pair well. Tall + Stout. Curvy + Square. Thick + Thin. Big + Little. Straight + Slanted. Light + heavy. Get it?
I've always felt rpg maker's menus were poorly designed. Partly because it's boring blue windows but mostly it's the fact that the text is the same size, color, shape throughout. In Japanese version they use a mix of numbers and roman letters, and a natural contrast between Kana and denser Kanji.
レオンハート
委員長 MP:777
Leonhart
Commander MP:777
I just noticed how Japanese characters don't get thicker when you increase the font size. It's so much cleaner. Edit: It's just that particular size. Still, to get the English version to match the weight like that in rpg maker would require extra lines of code to change the font.