Default No space for nandroid backup, options?

Hi,

I'm pretty new to nandroid backups so not entirely sure of the options I have with them.

I currently have a Moto G 16GB and don't have a computer so I'm very reliant on my nandroid backup in case anything goes wrong. But my current nandroid backup is 4.1gb and I only have 300mb spare and the Moto G doesn't have the option for external memory.

So I have a few questions and I would greatly appreciate any answers or any other options I may have.

1. Is it possible to create a nandroid backup on to a USB stick through USB OTG? If so, can you restore through USB OTG?

2. Is it possible to compress my nandroid backup of make it smaller by removing all user apps or not backing up any user apps in the first place (as I backup my apps to drop box with Titanium Backup).

Other options I have are backing up through USB OTG (if possible) then borrow relatives computer and copy nandroid backup over from the USB stick and push it to device memory through ADB.

Thanks in advance.

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