Something to consider:
A lot of women build a career first, then have a baby. They take off a few weeks, then go back to work. The baby is in daycare from about 6 weeks on. In my case, my youngest will be about 15 months old before daycare is even considered. I'll also have summers off.
Both on this thread and my journal thread, I feel like I'm being judged for wanting a career after living in the SAHM world.
My babies were in daycare from 13 weeks and 9 weeks (though part time on #2 there).
I'm not judging you for that. I'm just questioning how difficult it will be to do it with 4 kids. There's nothing wrong with having kids then building a career. I know lots of people who did that. My older sister was married with 2 kids. Worked some jobs here and there because her deadbeat husband couldn't hold one down for long. When she was a little over 30, she said "you are getting a job and keeping it, I'm going to school". Four years later (with her kids about aged 2-3 when she started, 6-7 when she finished), she had her BA and MBA. She's currently a company VP (and she's now ... 63? 62? I kind of lose track.) Still working because she likes it, and she did eventually dump the deadbeat husband.
But you have 2x the number of kids. Nothing wrong with online courses to start, but I'd certainly wait until most of the kids were in school before I took on more hands-on classes. I know almost nothing about nursing school (though a friend of mine just finished). I don't know anything about having 4 kids. But I do know life with 2 kids and 2 full time jobs. Your husband will have to pick up some slack. When my spouse was finishing his PhD (and working full time), I did ALL the chores for about 7 months and it SUCKED.