I bid a schedule of trying to work every thursday to sunday with two weekends off a month. Also allowing the scheduled pick up days to vary by 2 from this. I wouldn't try to bid a schedule with as many days off in a row. You will upgrade/downgrade/be junior/be senior. If you promise to hold "X" amount of days off for the rest of your career you'll shoot yourself in the foot. You won't be able to maintain joint custody with that promise. It's not worth the stress.
Your custody hinges on your ex's abiltity to see thru her own needs and realize the importance of you being in the childrens life. Married familys juggle schedules just as much as divorced. Don't believe for one second that you will cause them harm by having them live in two homes equally. When it is equal, keep it simple. Split schooling/medical/daycare 50/50. Clothes let em have a wardrobe in each house. Going tit for tat over little jimmy needing a another pair of jeans gets stressful. Instead when they live you, you cloth them and vice versa.
No one has a perfect work schedule. Never apologize for your career. It sounds like when you are home you want to be with your kids. Keep your head up, your kids will see in the long run that you love them.
The great thing about our career is when we are home we have NO work responsibilities. Make sure the Judge knows this. I love being the only dad, chaperoning the school field trips. When my kid gets out of school he isn't sitting in daycare for 2-3 hours waiting for me to finish my 9-5 job & commute. I'm there to get started on homework right away, after school activites etc. I'm never missing a school recital because of a late night conference call. They'll never have the excuse of forgeting homework, cause you're there to pick them up. You have so much to offer because of your career choice, don't let anyone spin it as a negative.
Good luck, my kid is a very happy child and I know it's because I'm in his life.