i do have to agree with the idea of starting with one from any stand point.
this will probably wander a bit.
foremost, like others, i have a specific body theology even though i do not practice a religion thta has any specific dictates. it's just what i dictate for myself. thus, we use NFP and abstinence. we have one child, and have been together 12 years. so, it works for us as a reliable method, but we are obviously open to any children that would come.
another aspect of this, though, is how we 'felt ready' to ahve children. at 26, i had an accidental pregnancy and miscarriage. this spurred us into thinking about what we needed in order to be and feel ready to care for children. we looked at every aspect of our lives and created discernable goals.
like the questioning i see in the OP, one of the things that i looked at was my self-image. that is, how i viewed myself and how i wanted to live.
this next part is not a judgment of how others choose to live, only my assessment of my *self* and how i wanted to live.
what i saw among other mothers and families was a life filled with clutter, women who had lost themselves in a flurry of children's activities and keeping up with the jones' children, and essentially a lot of stress. i saw that these women all dressed the same, had to have the same objects (cars, houses of a certain size, clothes, objects for babies etc). but what i also noted that while those things were supposed to make their lives easier, they actually made their lives harder. there were mroe things to keep up with, to clean or put away, more processes required for doing basic tasks (bottle feeding a baby is a *lot* of work!). it just looked completely overwhelming. it also looked ridiculously expensive.
so, i looked around and eventually came upon attachment parenting. i'll be honest, i really did assume that you "had to" do certain things like use cribs. i didn't even realize cosleeping existed. baby wearing? no clue. breastfeeding and home birth i did know about. i didn't get the house and car sq footage stuff. one baby requires 1300 sq ft and a yard? confusing to me.
but, i discovered unassisted chidlbirth, then a friend put me onto mothering.com, and that was that. about 2 years into my 5 years of exploring, i knew i'd found the way that i wanted to mother.
EC" fewer diapers. exclusive breastfeeding? it happens and you don't have to use bottles unless you want to. baby wearing? no need for stroller. cosleeping? not onyl up all night trying to figure out how to get a baby to sleep alone, but also no nursery needed--no bigger house, no crib, nothing.
so, i have one baby.
and it's amazing. i feel integrated. he goes with me everywhere--pretty much--and i baby wear and cosleep and breastfeed and EC and it's fab. i really enjoy it. he's well attached and happy. life is easy. we even have minimal toys. seriously, my life is ridiculously easy. it's easier now than before i had a baby in many ways. LOL
so, i found how i want to mother, and how it fits in with my minimalism and frugality.
but that leads us to that question of "how many?"
right now, my DH and i have started a business and we are getting it off the ground. it has massive potential to support us beyond our wildest dreams, and we are building it that way. but until then, it supports the 3 of us comfortably, though very simply (one bedroom apt, no car, not a lot of frills, but the basics to enjoy our lives).
we also live on the other side of the planet from family and we like to travel. that is probably our greatest family expense. day-to-day, we could easily support more children even now (money wise), but when it comes to how we like to live, one is enough for now.
there is also that consideration of time. right now, i can devote a lot of time to DS, and while he is very low maintenance (not at all high needs), i don't think i would want to care for a newborn now. it would be too much for me.
so, we are looking at waiting until DS is 4 or 5 to decide if we want to have any more children. by then, we'll have a firm grasp on how the business is going, we'll have travelled a bit with DS (back to the US, around NZ, possibly parts of Australia as well), and DS will be more independent of me at that stage. i can decide then if i want to spend more time with that little child phase, or if i want to just continue on in a family of 3.
at this point, DH and I are both leaning toward a family of 3, but open to having another child if we wish at that stage. but i'm seriously leaning toward not.
prior to having a child, we often talked about 2-4. now, we talk about one "maybe two" but not so much two.
not because of money per se, but because we are happy with one--and we feel that we can give all three of us the life that we want to live. we may or may not be able to do that with more, but we can't know that right now. so we are just not concerning ourselves with it until DS is 4 or 5 (2-3 years from now). then we can evaluate what we want with more information at hand.
but right now wouldn't be great for us.