I'm pretty new to media Jukebox too, but will try to help out a little here....
Upgrading to version 8.0.388 (latest version from d'load page) might help Q1 and Q3, but won't make any difference with regards to Q2.
1) The 1st time I ripped a cd, and chose the mp3 encoder option, MJ hopped online to go get the mp3 plugin, wierd, but i ran with it, plugin installed fine, no problems since. So, possibilities for you are, do you have the plugin? if yes, did it install OK? might be worth using the plugin manager to remove and reinstall the encoder.
2) CDDB will no longer work with MJ. Since CDDB upped the liscencing fees, MJ dropped support for it in favour of it's own database, YADB. I get the feeling YADB is in it's infancy, there's a few threads around regarding it's lack of results. I guess if we upload the cd info of failed lookups, the DB could grow into something useful, though imo, that process needs to be made a really trouble free process for enough people to use it. (ie. after manually entering track/album/artist info, pop-up dialogue; "Upload info to YADB - Yes/No?")
3) Not sure about this one at all, sorry. It's a feature I've never looked at.
I'm sure someone far more qualified than myself will be along shortly to correct any errors I've made above
The other thing that might help the pro's to help you, particularly with No.1 is to open MJ, click on Help > System info. then click the "clipboard" button, then paste it into your thread/post.
Helped a bit? hope so.
-=Marko=-