Your sperm donor will have the right to file a paternity petition in court and request a custody and visitation order. His name on the birth certificate will bolster his claim for parental rights. You're better off going through an anonymous sperm donor program.
You need to speak to a family law attorney with EXPERIENCE in addressing these sorts of issues BEFORE you do anything; getting this done right IN ADVANCE will be MUCH less complicated and expensive than straightening it out later if it's not done right.
It doesn't sound like he wants to be a sperm donor, but a father and share co-parenting with you. If you want a sperm donor, you should search for another known donor or go to a cryobank. If you proceed with this donor or another known donor I recommend that you and the donor meet with a psychologist prior to the donation (donor usually meets separately) and have an attorney who specializes in this field draft a contract defining all parties rights and responsibilities.