6) I learned something new---> blocks "filling up". So, please correct me if I'm wrong. The size of the blockchain is the sum of two parts: the mined blocks & the ledger
The blocks
are the ledger! The pre-Segwit 1MB block limit meant that the ledger can only grow by 1MB every ~10 minutes. Now with Segwit, the ledger can theoretically grow 4MB in ~10 minutes, though the practical rate is about 2MB/~10min and the current actual rate is only slightly over 1MB/~10 min.