Thanks! That makes a lot of things clearer.
4) The difficulty of each channel is independent of the other, and calculated based on the time since the last block for the relevant channel.
Is this adjustment actually happening properly? If so, what's up with all the 10-20 second blocks? Shouldn't the difficulty automatically be ramped up to stop them?
Go to the block explorer and click through a bunch of blocks, looking at the "nonce". You'll see lots of giant nonces like 376,227,383,918 but then you'll also see nonces of magnitude like 11, or 201, or 119. Those nonces are proof of hash mines that were so easy that they were solved with something like 20 to 100 hash attempts by a single miner. You can see this is true by looking at the hash value and seeing that sometimes only 3 to 5 leading zeros were needed.. Is that by design? Is hash mining difficulty supposed to be so simple?