I have mixed answers to your inquiry :

As per the first point, yes that's correct (but then again, unless you have other accentuated languages or unicode languages installed, you don't need to change the English file)

As per point 2, you need to do that only with fresh install

As per your last point, yes but somehow tables inside do not get changed unless you do them one by one.

I suggest you do a fresh install, start with creating you SQL database first and make sure that the collation is utf8-unicode. Then change the language file as you suggested in point 1. Then upload and install.

One last important point, make sure that all your files (for additional languages are encoded in UTF-8 not Ansi (if you are using Windows).

I hope that helps
Good luck!