OK, then it must be time to go for the nuclear option-depending on your budget, of course. Buy a Wireless HDD. They are not cheap. A 1TB wireless HDD will cost you about £120.
It will still be lots of faffing about to download the films from youtube, but, depending on picture quality and compression, you will be able to store absolutely loads on a 1TB drive.
It acts like an external Hard Drive, but you connect to it wirelessly via the wi-fi connection on your ipad, so no need for USB connections and adaptors.
To be honest, if that is one of the main reasons you want a tablet, then when it comes time to renew, DON'T buy Apple. You'd be better off buying 2 Android or Windows tablets, with USB sockets, and it would be absolute simplicity itself to do what you want to do. It only becomes a faff because you bought an apple product.
A Lenovo android tablet will set you back about £120, and comes complete with a USB lead! It has a storage capacity of 16GB internally, but this can obviously be increased by use of USB sticks , or SD cards, at relatively low cost. It won't be the same quality as an ipad, obviously, but would save you lots of headaches.