Looking to be a supportive working mom, any advice from experienced SAH parents ?

We're first-time parents in the US expecting in December. Our current plan is that he will be the SAHD until school- age. We're also hoping to have another child in the next few years.

He loves reading, exploring outdoors, is a good cook, and we both think he will be a natural ( or at least take everything as it comes ). If staying at home just does not suit him and he's miserable, we'll find some childcare and get him back to work (he's not in a specific career field and doesn't enjoy his current job). Even though I have a great career, I would definitely enjoy staying at home. I make about 4 times what he does and we would really have trouble getting by if he worked and I stayed home. We both work full time currently and I do most of the shopping / housework / cleaning and cooking - though I've been slacking a little on the meal prep through the first trimester ;).

I'm hoping to prepare myself for (A) how difficult it's going to be to go back to work after 8-12 or so weeks and both jump back into work and (B) be an understanding / supportive partner.

From those that stayed home -- what did your partner do that helped you stay sane? I want him to enjoy staying at home as much as possible AND plan to work hard not to resent that he "gets" to stay home.

ETA: From those who went back to work (especially moms) -- was there anything way harder than you expected? What did you do to stay sane?

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ETA a few details above.