First, If you are coming from Kubuntu, ie you prefer KDE, you might want to try Mint 4 kde Community Edition, beta 044. Even though it is still in beta it is pretty stable.
To answer your questions:
If the fonts you want are available for kubuntu, they can be used on Mint 4. Mint 4 uses the Ubuntu repositories.
No, you can have up to 16, I think it is, desktops. I am going to wing it a bit here because I don't have a copy of Mint 4 Gnome on my computer to look at right now. But I believe you can right click on the menu bar and select to add the desktop applet. Poke around, you will find it.
Not sure I understand the context here. Mint doesn't have an auto update routine like (K)ubuntu does. Actually, my personal opinion is that this might be a good thing. Things always seem to be slower, buggier, or just plain broken after an upgrade in (K)ubuntu. I usually recommend that when you install you use a separate partition for your /home directory. Then when you upgrade to the next version all your desktop settings and personal data structures will still be in tact. This makes for a more trouble free upgrade method. Of course that still doesn't mean you shouldn't maintain backups.
Yes all the drives and partitions should be auto mounted on startup by default.
Hope this answers your questions.