However, Aerith WILL be "Aerith" on both versions, no matter what the "Aeris" fanboys say
Then your restanslation is going to suck.
More seriously, I don't know who came up with the "it was supposed to be Aerith and Aeris is a mistranslation" idea. It makes absolutely no sense. ス can be either "su" or "s", or even "th", but since nowhere in official Square stuff it's ever written "Aerith" I don't see why it would be the "correct" translation because some random guy once decided it was.
I just saw a lot about translating names from Legend of Localisation website, and see how it is hard to translate names to/from japanese. However if Square decided to make it one of the possible ways I see no way someone could they were wrong for doing it.
PS : The reason I'm biased against the "th" is also because I'm not english. It's a sound that exist only in english and that is hard to reproduce and that I hate very much. It's basically a "s/z/d" with the tonge out of your mouth. Plain "s" is easy for everyone in all languages.