it seems every pixel art sprite creation tutorial focuses solely on the front/side of the characters, are there any resources on drawing the back of the characters?

Well in terms of sprites, isn't the back just the same silhouette as the front with just replacing the anatomy to be the back of the hero? If you're having trouble with making it look realistic, look up some anatomy references.. the internet has oodles.

The technique is the same of course - what you actually decide to draw is totally up to the character design. If you have any front/side sprites of yours that you'd like to post, we can definitely give you advice per character on a specific level.