I think the first thing that needs to be done is you need to know what to expect, in order to make informed decisions and to get a better handle on things.
Perhaps a local school will let you visit the special education class so you can educate yourself on the subject. A good friend of mine is a "special needs" teacher and teaches a dozen children with Downs, and she's had visitors with/expecting babies with Downs in her classroom before. Perhaps you know someone... or know someone who knows someone who teaches "special needs" kids and can help you to learn more about it.
Also, in my area, there is an apartment complex for adults with Downs... so they can be more independent. Many of the residents work at the thrift shop that funds the building and pays their bills, and they can find jobs elsewhere as well. They make sure they have everything they need so their parents can live their "empty nest" life knowing that their kids are all happy and in environments that are best for them. They spend lots of time visiting their families and go on trips with the others who live in the apartment building as well.
If I were you, I'd research all the programs and things they have for people with Downs, perhaps take a visit or just ask questions over the phone. Do lots of online research. I'm sure there are other forums just for parents of kids with Downs that you can use to learn more as well. Good luck with everything!!!