Drive

If you do not have internet (and therefore access to the live service) at home then you cannot do this as you will need to have your console connected to live in order to access the DLC.

However, if you do have internet access but not enough ports on your modem you can connect your console by bridging it through your computer.

support.xbox.com/.../win-computer

If what you mean is that you download DLC content on another console and then transfer it to a flash drive to your console if possible but the licenses that you download will be in the console where you will download it to your console and not to open DLC
will have to open your profile with that release or transfer licenses to your console. I hope I helped. Any doubt asmela know.

No you can't use the external drive as a system drive unfortunately.

Even if you could you still need your internal HDD for cacheing purposes.

Some games can only use the cache on the internal HDD on not on USB system drives.

You can't make it your 'system' drive. It should give you all of that 1 TB. Make sure it's format properly. There will be some items that you won't be able to move to your USB drive.

Well...I can make it my system drive, but it won't let me do that AND retain that 1 TB is what you are saying?

It let me make my 32 gb flash drive the system drive with no errors. The 1 TB drive gave me errors and only 32 gb of that space to use.

I appreciate your response Irixion. Just clarifying for my part.