How much travel is the "perfect" amount?

No such thing as universally perfect. We are all unique and bring different strengths, priorities and preferences to work with us each day; so what might be perfect for one will not be for another. With that context in mind, you need to decide what the right balance is for you and be ok with redefining that as your life circumstances change. I would suggest starting by writing down your personal and professional goals and values. If you see that you have a lot of personal goals outside of work that may require you to be closer to home base, then maybe you want to choose roles with less travel. On the other hand, if you have a personal value and goal to see the world and experience different places and cultures and nothing needing your attention at home, that matches very nicely to a role with a lot of travel! One thing I have noticed over many years of interviewing and hiring - many people who have been in travel-heavy roles for a long period of time want to take a break. This is especially true as they have more responsibilities at home, whether that is a position on a local charity board, a puppy, ailing parents or starting a family. Net is - don't look for perfect - look for "right for you right now".

The amount of travel is very dependent on your lifestyle. When I was first married and didn't have children, I traveled about 25% internationally for 5 years. Once I wanted to start a family, I changed roles, so that I could be at home with my young children. I currently don't travel anymore. You will need to consider your lifestyle. Also, domestic vs international and the specific locations and the activities that you perform once you reach your location might impact your decision criteria.

There is no magic number! It is very dependent on the couple; however, it would get more challenging to impossible whenever you have a family. Infasts need a lot of care.