Thanks for your comments.
I struggled with the pixel padding question and didn't come up with a good answer. I've seen spritesheets that have 16x16 sprites but with a pixel of padding so the grid is 17x17 but the padding was also fully transparent so you could cut the sprites at 17x17 and either use them like that or leave the problem of putting them back into a spritesheet to a different program. I tried out adding textfields but couldn't stand how they fit in with my theme of making the spritesheet take up as much room as possible. After the jam voting period is over I might take a hint from EZ_SUBS (another similar entry in this jam) and have textfields appear when you press Enter.