quitting after maternity leave

Erin
Hi moms,
 I was wondering if anyone has any experience with quitting their jobs after maternity leave. My husband and I have discussed it, and we think it will be best if I stay at home with the baby instead of working. I plan to work as long as possible, then go on leave. I'm just wondering when would be a good time to quit. I already planned on dropping down to part time when I get back. I figured I would work a day or two, then give my notice. 
I know I need to talk to HR about the legal/finance side of stuff- paying back benefits, etc.. The reason I plan to stay on is to save as much money before the baby comes and so there are no glitches with insurance coverage. I'm also not going to my boss about this because my position is very easy to fill, and my DM is already wanting me to step down to part time before I leave so they can fill it. I'm just trying to protect myself and my family. 
Thanks for any advice you have on this!