Nipple stimulation, like most natural induction methods will only be effective if your baby is ready to come anyway, for instance mothers that breastfeed through pregnancy can breastfeed right through until forty plus weeks! In was trying from 37weeks and bub didn't come until 37weeks and 4 days. I think an equally good thing to try is just lots of snuggles and happy times with your DP/DF/DH - it releases the same kind of chemicals and is much less painful. Also good for you to spend some last minute moments with your other half before bub comes along.

The prostaglandins (I think) in semen help to ripen the cervix - so if you can sex is said to be good to help the cervix on it's way.

It doesn't really affect breastfeeding - not that I found at least, and I'm sure if you google you can probably find some techniques.