Step parent adoption: No paternity established

Hi all, We would like some advise on step-parent adoption... I went through prenancy myself (no bio dad around), and bio-dad is not on bc. My son is 5 now and my husband has been involved in our lives since my son was 18 months. We have been married just over 2 years and my husband would like to adopt my son. We have questions about the process and are considering whether we should pursue adoption now or wait for more time to pass. Bio dad has never been involved, however he is aware that he has a child, but has never established paternity. We have had no contact, no support, no communication - nothing from him for 3 and a half years. We also do not know where he is, however we have not conducted an extensive search. Our question is about whether or not we are required to contact him for the adoption, given that there are no paternal rights that need to be relinquished? Second question is, if we are required to notify him and include him in the process, could we claim abandonment on his part? How difficult is that to pursue? We're really trying to figure out how to proceed with this, and whether or not the timing is right. We would appreciate any insight... Thank you much.