These ideas sound cool, I'm psyched to see them take shape! I feel like this is the sort of thing that makes System Fictional seem cool to me!
There's a good collection of free public domain art here, although I think it might be hard to find anything that works for super sentai. https://newschoolrevolution.com/public-domain-art
Also for free layout and image processing software for an old laptop, have you tried google docs and slides? They are pretty powerful and can get you a ways. They have a decent built in font selection.