I first recommend trying a fresh ui settings rather than trying to import them from an old pc, that should bring the persona bar, etc. back. Make sure you're doing a fresh install of Fetish as well, I've had no other reports of what you describe in #3 as well (though I personally don't use a merc, so I wouldn't normally notice any issues with that window).
If the PersonaBar doesn't show up with the fresh install / fresh ui settings, try /show_window MainHud.Personabar, that should force it to show.
For #2, you need to make the changes in the _Fetish_mainhud_raidabilities.xml file if you want them to stick - Fetish was never coded in a way to save changes made in-game; getting them to save requires a good bit of trickery and I honestly don't have the time to devote to try and revamp it. I don't play a huge amount anymore outside of raiding a few nights a week.