I believe that at the end of the day/life, etc. you will only regret what you didn't do/try, and I seriously doubt you can regret being a FT mom. It just seems so... innate.
(WARNING: Thread Hijack) MrsCoolCat - I think you made many good points in your post, and I love how much you've thought out how you want to parent and are making plans to make it happen, and how supportive you are of the OP. I offer the rest of this in the spirit of of openness, trying to be helpful, and sisterhood...
I invite you to question the beliefs quoted above. It is absolutely possible to regret staying home with kids (I know several women--felt like they lost their identity, life circumstances changed and they needed to get back into the workforce and found it difficult, years of lost career growth, isolation and depression and after the fact thinking their children would have actually been better off in daycare). I'm not saying it's common, and I'm not saying there aren't things you can do to mitigate any of those risks, but it is possible.
Also, I encourage you to think of ALL moms/dads as FT moms/dads (once you are a parent, you are a parent 24/7, regardless of what else you may be doing with some hours of your day, and that's true whether you work outside the home or not). I'm also not sure that wanting kids, wanting to be home with them, etc. is "innate." It may be innate in you, and you may find it impossible to fathom feeling any other way, and it may even be innate in many/most women, but it's not universally innate, and it's those kinds of words/phrases that seem innocent enough but can (completely unintentionally, I'm sure) offend/marginalize women like me, who feel differently, and who have made different choices, and yet still consider ourselves full-time and darned good mothers and women.
If you truly believe that women who work outside the home are somehow "less" of a parent than SAHMs, and that women who don't actually
want to stay at home are unnatural, then please disregard everything I said. :-)
To the OP--congratulations! What an exciting, marvelous journey you are on. You sound well-suited to being a SAHM (introverted, not getting much intrinsic value from work outside the home, and desiring to be home with the baby), so I think you should do absolutely everything you can to make that possible,
while also keeping your options open. That's actually my advice for all moms--keep your options open as much as possible, because it's difficult to predict with 100% accuracy how you're going to feel, and your feelings or circumstances can change over time. So for working moms, that means don't build your lifestyle up to the point where it requires two full-time jobs to support, and for SAHMs, that means intentionally keeping your skills and relationships/networks current in case you need to, or want to, go back to work.
In an ideal world, there would be lots of support and options for all parents, to work full-time or part-time outside the home or not, to do paid work from home or not, to enter and exit the workforce as it suits their family's needs. We're not great as a society at doing that, so it's up to us as individuals to try to keep as many options open as possible and seek the support wherever we can. You've gotten great advice and support on this thread, and one of the awesome things about Mustachianism is that it shows us we can actually live on less than we may have previously thought, thereby providing options. It's pretty darned cool. Good luck with your decision!