Cheat Sheet

tile         8      16          32  48
player  16  32      48      64 128 
screen 144 180 270 360 540

The sweet spot for action pixel art games usually falls between 8-16 tile sizes, 32-48 character sizes and a screen height of 180-360.

Examples

celeste

Celeste is a "core platformer" meaning all the things you do in the game involve jumping on things, jumping around things, and getting through the level. No sword combat, picking up objects, etc. As a result the character size relative to the screen height should be pretty small.

tile     8
player  18 (10% of screen height)
screen 180