Here's a tip: Keep that Fantasy in your head ^_^
Here a short explanation why.
It was attempted about five years ago by a Japanese guy using the MMC3 memory mapper and a new engine he wrote from scratch. He abandoned it after a year of work when a beta tester posted his rom on the internet, wasting all his work. He had a new battle system, new music, scripting, and a materia system in place. Don't bother looking for the rom, it's gone off the face of the internet
Here is a longer answer
The FF1 engine has many shortcomings making it ill suited for what you want.
1) You can't "pick" your charaters exept in the beginning of the game. Having two Clouds, an Tifa and an Arieth is lame. (Fighter Fighter, Monk and White Mage)
2) The world map requires you to follow the contours of the original FF1 map or it will mess up your map viewer, unless you plan on rewriting that.
3) There is no event system. You set flags to make things appear/dissapear on the world map (bridge, airship) to allow passage to other parts of the game.
4) The conversation system is very simplistic and non-scriptable
5) Inserting music will require you to write a tool to convert the music into a format the NES can understand. (Note, I said NES, not FF1, as the music system is also hard-coded)
6) You can only have a maximum of 999 hitpoints and 50 levels
7) You have no ability to do an MP-based magic system, and must use FF1's cast per level system
8) you can't make a summon
9) The battle math is wildy different, and also hardcoded. Do you plan to re-calculate the experience curves? You will need to make a algebreic function to do that.
10) You can only hold what is avialible in the two map banks. You have less than 16k on the world map with RLE compression and, I think, 2K per each town. That's not a lot of room.
11) Yor tems are limited to tents, potions, armor, weapons and key items. The key items only set flags so the engine can turn on and off things
12) you only have sixteen banks of 16k on MMC1 (256 K). FF3 uses MMC3 that can use 32 banks of 16K (512k) not only that, you can do summons in that one.
Your best bet is to rewrite a new engine using bits of code from FF2 and 3. You will quickly find that in the end you will be making a FF1 clone, not a FF7 one. The engine is just too limited.
Why do all that work... Just grab this...
http://disch.zophar.net/ffhackster.htmlThere is no reason to re-invent the wheel.
Let me know what you make.
P.S. I took a year out my life to reverse FF1's source code. I had it 80% done before I lost it in a hard drive crash. Of that I only had 10% of the kernel done. I abondoned the project before the crash as I learned Square was going to make FF1 for the PSX anyway.
In short, unless you rewrite yor own engine using a larger system, it's not woth the effort.
As an addundum, probably thousands of people before you have tried this, including myself. It's just a Fantasy.
I invite you to prove me wrong however,
