Questions about adoption?

I'm pregnant and could never go threw an abortion. I have 2 children already and make just enough to support them. Another baby would result in less for them I want to send them to college if they choose to go and buy there first car and there wedding (i have 2 girls) I feel my girls AND the baby would be better taken care of if I thoughtful adoption for this new baby. Were do I begin? Social services? How long should I wait (as to not disappoint a couple if something went wrong since I'm only 4 weeks in) could I be involved in the choosing of the parents so I feel my baby is in good hands? Any information on this subject is helpful thank you!