Hi Riab, yes, I think I was thinking (in that less than crystal clear way one does after midnight) that the sensible thing would be to require anybods who wanted to be legally paired off to form a civil partnership, and keep the religious (or for that matter humanist / existentialist / whatever) marriage a separate ceremonial , non-legal affair.
Apart from that, I agree with bibliophile, how much of a fuss you make of 'your day' is entirely up to you & yours. I've been to church weddings with meringues and full choirs and others with half a dozen people in the front pew. One civil wedding I went to took over an entire country house hotel, while another took over .... a London black cab
As for the children, my hunch is that what makes the difference to them is how committed their parents are to each other, irrespective of bits of paper. If your parents are committed to staying together & working at their relationship with each other, married, partnered or not, they're surely more likely to work at their relationship with you the child(ren), besides providing good role models for 'how to be an OK human being'? Getting married / civilly partnered is surely just a (probably not highly accurate, given the divorce rates) marker for some degree of commitment.
You can do the same thing on a DIY basis with parental rights recognition, wills, joint tenancies etc. and I know people who have done, and just had a big party.
Mind, some of the DIY can be a right faff - a few years back a friend had to adopt his own children in order to be legally their father, because although he and his partner had been together for over 10 years, they were not married (& had no intention of becoming so). I know the law's been changed since then - good thing too!