Time management, as said above. Set it up for success from the get-go. You are wise to be thinking through this now while you are still in college.
You need a career, as well as a job and a boss, that allows more flexibility in adjusting your work and off hours. Sounds like you are on the right track already, generally speaking. Do NOT get into an office-bound track such as accounting or customer service (or management!) that is not time flexible. They not only expect standard hours and days, but you are under the eye of boss & co-workers in a culture of putting in the hours, regardless. Do pursue sales or tech jobs with work-at-home capabilities. Even offshoots to the financial industry that have you out of the office and mobile, such as property inspections, appraisals, so long as your location and time aren’t constantly monitored. Being able to put daylight hours to riding and other hours to work will help a great deal.
You need a field that pays well for individual work without depending on promotion to management. Management can be very difficult to time-control. Unless you become ceo of your own company!
Avoid anything that will lock you into a lower-income strata than you need to be in. If it doesn’t pay well, strike it off your list (you should do that anyway as your work should be appreciated and rewarded).
What the others said above about how much time you have for what in your life. To pursue your riding as seriously as you would like, you may become a work-barn-work-barn machine. You won’t be able to make ongoing commitments to community, charity, church, other interests/hobbies/activities, just an occasional one-off activity here & there. You will know non-horse-people less - you won’t even be in places where you can meet them, outside of work! Relationships and family will require understanding and compromise, on both sides. All that has to be ok for your life.
You can also choose certain times of the year when you are all-in with riding and competing, and not so much the rest of the time. You might choose a year when you are going all-out for year-end awards, but not maintain that level of effort every year.
And last … do it EARLY in your career. Don’t let riding jeopardize your first jobs, but do this NOW, before you are anchored by family. 
:winkgrin:
Plenty of people manage their children, their horses and their competitive riding, and have sweet pictures to show for it. BUT … bottom line, if a toddler is with you, or even an older child, you are first a parent and second whatever else is going on. Meltdowns and mealtimes will end up taking precedence at the horse show. You will be limiting your horse-outings, just because of the massive logistics of having children and family there with you. :yes: So - go for it early, build your memories and satisfy the itch while you can more easily do so.
You sound like a wise and thoughtful designer of your own life. Have a good one! 
