BA does not interline to AC on separate tickets (and AC doesn't interline to non-Star). So you are stuck with separate baggage check-in with all your options (BD would interline with AC, so BD to DUB would be the most viable option). But AC is taking a hard line with missed flights on cheap tickets recently, and probably would make you buy a new ticket if you missed the flight check-in cutoff deadline (I *think* it is 60 min at DUB, but you would have to check with AC, it might be as much as 120 min). Given the scenario, an overnight at DUB seems mandatory unless you can take BD and check the baggage through.