You're probably going to want to define a slide up note that uses the linknext property to link to a slide down note. There are thorough tutorials on the subject on the forum.
It's possible that UTF-8 lyrics can import, but EOF's font wouldn't have a way to display it. It's possible that it could be made to export the lyrics back to XML intact (if it doesn't already), since the XML file is written as UTF-8. If you have an existing lyric file I could test with it.
This is usually an error during Guitar Pro or Tux Guitar converting the tab to GP5 format. EOF will try to complete the import, but it's possible there are some timing problem that will result from this. You may have to make some adjustments after it imports in EOF.
The original EOF developer made a new Mac build of the current source code. I uploaded it to Ignition. Please give it a try and let me know if you run into any problems.
There isn't, and I don't have a way to make a 64 bit Mac build. Emulating it in a virtual machine (or dual booting Windows) is going to be the best option for Mac. If you really can make use of a 32 bit Mac executable (ie. you're still using Mac OS Mojave or older), let me know.