You have covered a lot, I'll address the double spend in this post.
Double spending isn't so effective on services, because they require multiple confirmations to credit value to your account. If you made a peer to peer trade, and somehow were able to double spend AND get away before the network caught you, you would have the coin and the cash. And an angry buyer to deal with, but that's a separate issue.
You could trigger the secondary, double spend transaction remotely after you make the first "show" transaction. You might want to make a deal with a node, so you know the second transaction reaches the network before the first. Or put a nice fee on it, if the fee isn't the same size as the send, you should profit regardless.
With how weak the mining is on some of these coins, you could try a majority attack if you have more than 51 percent of the network. That way, your nodes decide which transactions make it into blocks; you can simply pend the honest tx until you get home, and double spend with the bad tx, or simply deny the honest tx period.
Again, you just pissed off a real live human being that has seen your face, not an internet gangster. You will have to deal with a buyer that may be
inconsolable Pai Mei was inconsolable, if you are a fan of Kill Bill
Back in 1003 ("one-double [n]aught-three") in China, as Pai Mei was traveling down a road, a Shaolin monk crossed paths with him. Pai Mei gave a slight nod to the monk, who did not return it. Although the motives of the monk remain unknown, whether it was an insult or a misunderstanding, Pai Mei tracked him down at the Shaolin Temple. He demanded that the head Abbot kill himself as a means of retribution, but the Abbot refused. Consequently, Pai Mei single-handedly massacred all sixty of the monks residing in the temple.Dont get killed by Pai Mei.