Q: Can't install windows through bootcamp (Imac Mid 2011)

Hi, I've been struggling for the past 2 days and can't seem to find how to create a windows partition and have it installed.

Note: I have a 27 inch mid 2011 Imac and run MacOS Sierra 10.12.

I'm having issues with bootcamp especially at the USB drive step of the process.

1. I don't understand why Bootcamp assistant only display 2 tasks being #1 download windows software and #2 install windows 10 when all apple support pages show 3 different tasks available like here https://support.apple.com/en-us/HT205016http://

2. I'd prefer to install windows 7 on my partition, however bootcamp says "install windows 10", does that mean I cannot install an older version on my partition? I've tried to install windows 7 through an .iso win7 file AND a .iso win10 but none of them works.

3. Whenever I try to install windows, the system don't recognise my USB drive (would it be with win10 .iso + associated drivers or Win7 .iso. + associated drivers), and constantly ask for a disc to be inserted.

My USB drive has been formatted via Disk Utility as a MS-DOS (FAT32) volume and all .iso used comes from Microsoft. I don't understand why I cannot seem to have my .Iso recognised by the system....

Help please:)