Unless it's been fixed yet, if you've already imported from LJ, trying to import from IJ will result in dumping comments onto the wrong posts b/c of the way the importer works. So, I would suggest holding off on that until there's an update on the importer. (I found this bug when I was testing the importer, so I know that it actually happens, but I don't know if it's been fixed yet or not.)

The auto-complete for tags - it works for me here too.