Adoption in Halacha

Is there a mitzvah for a childless couple to adopt?
Are you מקיים פריה ורביה with adoption?
Is there an obligation of חיוב כיבוד אב ואם towards an adopted parent?
Balancing obligations to the natural parents VS the adoptive parents
Does an adopted child say Kaddish for his adopted parents?
How is an adoptive child called up to the Torah?
Adopting non-Jewish children VS Jewish children
Is there an Issur Yichud with adoptive parents? Hugging & kissing?
Do you have to reveal they are adopted?