I think a "spitefire" among Havanese is probably still pretty mellow compared to the "average" Jack Russell or Border Collie... Or even Aussie, from the dogs I've met of each breed.
Kodi was a pretty out-going puppy, and had plenty of energy, but he was not near the "handful" as other breed puppies in his puppy classes... In fact, as with many of the puppies we hear about on the forum, he tended to be "the star" in puppy classes.
As he mautured, he also mellowd out even more. He has ALWAYS been up for a good romp, but is not demanding about it, for the most part. He does consistently want "play time" in the late afternoon, early evening, but throwing a ball or toy for him for half an hour is enough to settle him back down for the evening. He also either goes on about an hour walk, or does an hour class most days. (sometimes both). But if it's bad weather, or I'm not feeling well, he's perfectly content to just hang out for the day.
Last summer we traveled to Canada with him, and we were often in the truck, with him confined to his seat with his harness for six or more hours. He did fine! Obviously, we stopped for potty breaks and to stretch our legs from time to time, and I often took him for a walk while Dave set up the RV when we arrived at our destination. But he couldn't have been a better traveler! I know that one of Kodi's litter mates lives on a boat for much of the year, so he must be a good traveler too!
I think that a very mellow puppy would adapt to TRAVELING fine... But it would depend what you want to do when you get there. If your idea of vacation is a lot of sitting around in deck chairs, that very mellow pup would probably be a good choice. If, like us, you want a dog who enjoys going off on hikes in the woods or running on the beach when you arrive at your destination, a pup with a little more energy might be a better bet.
More than energy level, if you want a dog who loves to go places with you, I think you want to avoid a shy puppy, and even with an out-going one, as other people have said, socialize, socialize, socialize when they are little. Also, make sure they are in the car, riding with you, OFTEN to get over any possible car sickness issues. These trips can be very short in the beginning, but make sure they get used to the motion of the vehicle.
Finally, IMO, it is IMPERATIVE that a dog who is going to travel with you extensively be crate trained and trained to some sort of indoor potty system. There will be times that you stay at a hotel, and need to leave tour pup in the room while ou go to dinner or whatever. Many hotels require that the dog be crated when left alone in the room, and they don't tolerate a barking dog. So your dog should be able to wait quietly and happily in his crate until you return. An indoor potty option is WAY easier when the dog needs to pee first thing in the morning and you are on the 12th floor of a hotel!
These are things that can be taught to any puppy with time and patience, but it will be easier with a confident, non-anxious type puppy. This, to me, is more important than energy level. You can have a high energy, very anxious, shy dog (probably the worst combination in any breed), or a high energy, supremely confident dog. The same is true with low energy dogs.