For spacing between siblings I can say that my daughter and son are 23 months apart. She never had any problems with sibling rivalry, he just seemed to "fit" into our lives. On the other hand, our son and the new baby (due in October, also a boy) will be almost 2 1/2 years apart. I have some very real worries about my son's adjustment, as he just doesn't seem ready for a new baby (I know, a little too late); he just seems like he's much more immature than my daughter was at the same age.
So, although I can't speak for the age of your husband, I would definetly look at the maturity of your son rather than just an age for child placement.
Homesteading Mama to homeschoolin' kiddos London (10) ; Alexander (8) :; Holden (5) :; and Sergei born at home 8/18/08