New to hacking. Need advice

Most of the editors can be found here but FF3usME is the most complete one. There is no guide for this editor. The best way to learn is to practice.

As for advice on how to start a project, well it depends what you want to do. If you want to do a complete hack with new events, items, monsters and characters I suggest you keep a log of your changes or excel sheets whatever suit you. Also if you want others to play your hack, I suggest you come up with originality such as new events, new songs or ASM changes. A hack only developed with the editor might be good but will lack originality.

If you have specific questions about the editor(s) or any other thing, don't be afraid to ask.