After spending a couple of years traveling on and off after quitting a job, there are a few things I wish I'd known/asked myself beforehand.

1. In your daily life, are you typically happy/comfortable not having a schedule? You might say "I'm traveling to get away from daily life," but longer-term travel is not like taking a vacation. It's much more like daily living. If you're happy not having a schedule in your normal life, don't plan much when you travel. I didn't even ask that question before I went traveling, but by nature I have a hard time not having a plan so I planned the s* out of my travels (I picked destinations around the planet, bought plane tickets to a chunk of the first destinations, planned activities/goals along the way and even had future destinations in mind (zoom out on Google Maps and just dream/lust after places! You'll almost immediately have a plan even if you don't like planning!). Anyway, I'm super stoked I planned the trip. I would've been a bit bummed if I hadn't, but as some posters here have said, planning isn't for everyone and you have to know what you like. And of course you can have a bit of both. Doesn't need to be "no plan" vs "plan every day," but structure, if you enjoy structure, is key. If you are too structured and are traveling to change yourself, of course ignore this advice.

2. Do you feel a need to accomplish things? I'm just going to go out on a limb since you're asking this on HN that you like "getting stuff done." You might be an "enjoy the journey more than the destination" person, but a big part of the journey is progressing/growing and so, again, related to schedule, plan on actually accomplishing some things while traveling. My partner and I, though not particularly outdoorsy, took advantage of several months of traveling to do some short, but serious (for us) hiking and I have to say that absent those events during our travels we wouldn't have enjoyed it nearly as much. It's awesome seeing the world, and talking to the people who inhabit it, but the desire for accomplishment doesn't go away when you do longer-term travel. Like I said, it's not like a vacation (though of course we were happy to find ourselves on nice beaches after pushing ourselves to reach "the top of the mountain." And your mountain can be hiking, learning a language, building an app, volunteering, etc. We just happened to want to see some epic nature)

3. Does my partner "love" me enough to not kill me if we're on top of each other for months on end (and vice versa)? You can only ask this, of course, if you're planning on traveling with a partner. You can always take breaks from each other, which is likely easier if you're traveling with a friend instead of a romantic partner, but I think saying upfront what you're both comfortable with is important

Apologies for the long post. Not sure if you, the OP, will read it, but if you want a spreadsheet with an around-the-world budget, hit me up and I'll share a Google one with you. I think I still have it. The single longest trip we did during the 2 years was three months (far shorter than a bunch of the folks who commented), but I/we stayed almost right on budget the whole time, which is actually much easier than you might think because as long as you have some flexibility timing-wise you can always save money on the big-bucket items (air/travel, lodging, food).

Oh, one last comment... If you love travel, and have dreamed of doing it more extensively and think you can pull it off, just do it. The only frustrating thing about traveling (for people who really enjoy it!) is not being able to do more of it.