i probably wouldn't do that. there are so many things that can go wrong - lots of breeders on here will have had babies & sometimes mothers die. you may need c-sections, mum can die from ruptured womb, the babies can get stuck in the birth canal, there can be something wrong with the babies...
my first lot, fluffy had mastitis and we had to hand feed them for about three weeks - for the first two weeks that meant feeding every two hours, day and night & a feed took approximately half an hour so you got about an hour of sleep between. it being knackering aside, you were always really worried you'd find of them dead next time you go in. thankfuly they all pulled through and fluffy took over once she recovered.
you got really attached to your boys, how do you know you won't get attached to the next litter? if you're like me, you would! and imagine, if you have to handfeed the little monkeys to keep them alive, would you be willing to part with them?
also, i think the general advice is no more than two litters per year, lots of people will not have more than one. so the mum and dad would not be able to be together for that long and you may not be able to reintroduce them after a break.
do you have a pedigree for these chins? to avoid any genetic trouble, you should know about any medical problems in the past five generations. i don't have this for mine and while neither of them has had any health problems, their relatives might have. it's something i do worry about but hopefully the babies will be ok.
i know you said it was pretty clear when she was about to give birth but if she only has one baby in her tummy that's quite small, you may not even be aware that she's pregnant. and then on the opposite side of the spectrum, remember litters usually go up in size (mine went down from 3 to 1) and can go up to 6!
as for mating behaviour, i remembered that chinchi had a bruised nose at one point and i thought he must have nose dived. i don't know if it was 4 months before she gave birth the first time but i think it may have been a result of mating. however, the second time round, there was no fur slips or anything that would suggest they mated. then again, i'm not an expert - i never intentionally bred