A quick update here.
After leaving my machine synchronizing the mirror during all my holidays, I finally have all the files locally.
I'm adding them to IPFS, which brought two unexpected problems. First, the recursive add will take a little more than 12 hours The Ubuntu mirrors are supposed to sync every 6 hours, which will not be possible with IPFS. We will have to sync it only once a day.
Second, ipfs stores local blocks for each file, so that duplicates the amount of space required for the mirror. The main mirror, instead of ~2TB will require ~4TB. As suggested before, the others can just sync the IPFS blocks so they will still require ~2TB.
I'm now going to package the transport into a PPA so it will be easy to install, do more tests with my local mirror and continue trying to find a server with better bandwidth, and experiment with bitswap to sync multiple mirrors.