For the swap, you should be able to use the taint method so that the BTCs and BTUs get to their proper destinations:
Yeah, your method seems fine. Although since it's such a large amount of money, I'd also add something like a "<2years> CHECKSEQUENCEVERIFY" that allows some escrow-agents to resolve the dispute if the two parties don't 2-of-2 sign before then.
You'd also probably want to do a coin-join style send to the escrow address -- just so the first sending party doesn't risk getting trolled and have their money stuck in limbo