Answer to question1: if you delete Linux and want to not affect the windows bootloader then the Windows bootloader would have to manage both OSs.
Question2: sda, sdb, sdc ... you see a pattern? Everyone is a separate partition, and this is their name. In windows you have C, D, E ...
To make what you are asking I would do like this:
Enter in Linux and do 4 partitions:
- sda formatted as ext4
- sdb formatted as linux-swap (with the space double of your ram in the system)
- sdc formatted as ntfs
- sdd formatted as ntfs
First instal Ubuntu, when you install you select the mout point / in the sda and then the sdb as swap partition and you install.
Then, install Windows 7 and you will see you have 4 partition in which 2 as ntfs and and probably two unrecognised. In Windows you will have the C drive where the Windows is and the second where you put your data.
Since the Windows 7 is installed secondly and because Windows does what it wants, it will put its bootloader over the Linux one.
Now I have not done lately this (2-3 years ago), and I may not be the best practice, but you get the point.