As much as we all wish we could "have it all", there comes a time when we have to face up to the reality that we cannot have it all. Sacrifices have to be made in order to maintain our health and overall quality of life. Personally, I feel that health and family should be made a priority over working outside the home.
Plan carefully and make wise decisions. Learn how to budget your energy and your financial resources. You may find that working outside of the home won't always be a possibility for you. Don't be afraid to ask for help when you need it, and be sure to have a support system available to you (family, friends, etc.) who can help fill in the gaps when you have to do a tune-up or something.
Remember that even people without CF often fall far short of being able to "do it all." Don't put undue pressure on yourself, it will only backfire.
Best wishes