Re: At what age/ weight did you stop wearing your baby?
I would personally keep 1 and sell the other.
I still wore my son until 3.5 pretty regularly. Beyond that though, if you're planning on adopting I think one might really come in handy for a few reasons-
1) babywearing is an awesome tool to help facilitate bonding between adopted children and parents (esp if you wind up adopting a toddler/preschooler)
And 2) with a new addition to the family your son might crave the extra snuggled that babywearing can provide.