I'm planning to go to Vietnam, Laos, Indonesia, and Hong Kong for 18 days total (about 4 days in each country) in December 2017 or January 2018.
First of all, I think this is a really bad idea, mostly becuse of the (about 4 days in each country) part of the plan.
But you could do it, if you just stick to one place or city in each country, and do a few day trips from your town or city. For instance you could go Hanoi - Lunang Prabang - Ubud (on the island of Bali) - Hong Kong. The flights between Luang Prabang and Bali would take a whole day to complete.
What you'd do is decide on your travel dates, then book a series of one way flights between each airport. It won't cost any more than the enourmous headache of trying to book the whole thing at once.