So I'm working on a game that's basically an homage to Final Fantasy I & II: Dawn of Souls. (It's not a fan game).
The game is going to use an art style similar to that which is used in FF 1&2 for the character and battler sprites. They're still drawn from scratch, and aren't replicated or traced versions of the original sprites, but the intention was to have an identifiable classic final fantasy aesthetic to them. I also plan on indicating my source of inspiration in the game's credits.

(Leftmost sprite is Firion from FF2, the one next to him is a deconstructed version so I know what pixel patterns to avoid. The rightmost sprite is the end result. The bottom row shows Firion, my sprite, and the two laid overtop of each other to show any similarities/differences)
Edit: Put together some comparison shots of the animations just to be sure.
Firion's FF2 Animations
My Animations

(Left and right sprites are rips. Middle sprite is mine.)
I feel it's also worth mentioning that the game uses a variety of freely obtained royalty free music. Some of the songs are free to use in commercial projects, while others require you buy a license.
I don't have any plans to sell the game. It's going to be free to download and play. But I started thinking of the possibility of selling a digital art book after release if people really enjoy it. The art book would just contain stuff like original concept art, full character busts (also original), and some developer commentary and anecdotes.
Would selling an art book for this game be an acceptable thing to do, as long as none of the character/battler sprites are in the art book? Also, would I need to purchase commercial licenses for the songs that require it as well, even though the game itself is free? Edit: Got my music situation figured out.