Glad you made the decision to try out new things. There are many other operating systems other than Windows and GNU/Linux based distributions are one of the most popular. Ubuntu is a good one, there are others like Linux Mint and many others to suit your need. I personally use CrunchBang Linux on my 1GB system. As for your questions:
1. Not necessarily. Windows and GNU/Linux uses two different File Systems
. PC's use FAT/NTFS while though GNU/Linux can use any one, usually ext4 is used, which is the best one in my opinion. If you have 200GB of unallocated space and you are using all of it, later you can unallocate some of the free space used by Ubuntu and swap it with Windows. To do this, all you need to do is create a partition of how much space you want to give Windows, then format it to NTFS. You DO NOT
need to delete Ubuntu for that. But doing it this way will make Windows detect it as another drive (it will have another drive letter). Or, as you said, you can delete the Ubuntu partition, extend it to an existing Windows drive if you want to have the same drive letter. Then install Ubuntu again. Just a note, Ubuntu needs merely 6GB to funtion properly.
2. No, Linux uses a completely different method (File System)
3. Usually Ubuntu handles hardware really well, I have never needed to install any drivers to get anything working. You will need to get the Graphics drivers though. If you want added functionality for the mouse/touchpad, you might need to install drivers for that as well.
4. No, GNU/Linux can read data from all Windows drives (FAT/NTFS), but Windows cannot read data from GNU/Linux drives (ext4). You can use Ubuntu to play songs from the Windows drives.
5. It is generally recommended to install GNU/Linux distros after all Windows OS'es have been setup. Although the other way around is possible. Windows has a hard time letting GNU/Linux distros to show up in the bootloader. If you want to install another Windows OS, do it first, the GNU/Linux. It will save you a lot of hassle. If the 3rd OS was a GNU/Linux distro, you won't face a problem.
Edited by Babbzzz, 17 January 2014 - 07:23 PM.