Click on the Finder's icon in the dock, and then look at the very, very bottom of the window that appears. You will see a count of the items in the current window, and the amount of free space on that drive.
Hotmail won't let you access your mail from anything but hotmail.com. For Gmail, log onto gmail.com and click on POP mail (or something to that effect) and they instructions of setting it up in Mail. Not too complicated.
And yeah, on a Mac most programs don't have uninstallers, you just drag 'em to the trash, empty it, and you're done!
Yep. In the vast majority of software created for MacOS X, any necessary support files are included in the Application bundle itself (the icon you see when you open the application). There is no populating of system directories with frameworks that get left behind when you trash the app.
There are exceptions, notably in the cases of software that extend or add system-level functions. Stuff like ShapeShifter, USB Overdrive, Palm Desktop, VirtualPC (with its virtual networking switch)--they will all install additional Kernel extensions and/or frameworks that reside in the root /Library or /System/Library folder. Software like this comes with an installer, and running that installer will give you the option of removing all these support files. If you trashed the installer, just re-download it.