yes - booking flights really early ahead to get lower prices, although you often hear people claiming it is a good idea is very overrated. It's not necessary at all, and prices can be not much or no different when booked a week ahead to months.
agree axe Boracay, it's not bad if you are a first timer in Asia but you're not. Forget about getting the ferry from Manila to Palawan too. There's no point in it at all. It's awkward because ferries are few and it also takes ages too. Far better to fly.
I assume you know there is no direct flight to Vietnam and you'll have to route through Manila where to be safe, we usually recommend that you spend your last night there just in case your flight up there is delayed or cancelled.
but coming in, spend the least amount of time in Manila that you can. If you arrive at say 10am, aim to get a flight out of there at about 2pm. Even you arrive late at night, it's probably best to get a crack of dawn flight out rather than spend the night there.