Here are files you might like for your emulation needs. As always, we don't claim to have the most recent version of all Final Fantasy I emulation files here - where possible, we'll also give you a link to the home of the project so you can check yourself!
From our old affiliate, one time host, and now-defunct OPGaming comes Final Fantasy Revolution PLUS. This hack was quite ambitious and changed a large, large portion of the game. Definitely worth a play! As all our hosted hacks, you need to have an IPS patcher, which we neither provide or officially support, sorry.
Version 1.11 of a nicely done hack by Frionel; a complete retranslation and smoothing of the script and event displays makes for a much nicer play than the original NES version. Progress on this hack is now nothing at all, sadly, but it is nice to have nonetheless.
This Final Fantasy Hardtype, created by Ultimate Evil, exists just to punish those who didn't think the real NES version was hard enough. Good luck with this one.
A nice change of pace hack that edits FF1-Japan images into the NES English translation, and even changes some of the script to make it more true to the original.
There are a lot more hacks out there, we've just selected a few. We suggest Google to find more.
For NES emulators, you have a ton of choices. We've selected two here, but there are many, many others, so feel free to look around a bit.
Try them both, and make your choice. Since the emulators will be updated periodically, we link only to their homepages here.