My question involves adoption law for the State of: Illinois

I'm a mom to one 3 year old boy. His father & I broke up when I was about 4 months pregnant & wasn't there during the birth or afterwards. When my son was about 4 months old he saw him a handful of times, but never contributed financially, or as a parent (I.e. spending time with my son, taking care of him, etc) He went a whole year & a half with maybe 5 visits. He came around more when my son was about 18 months, but he went out of his life again 6 months later. Still never bought my child anything, nor helped pay for diapers. He watched him a few times, but he always reluctantly did so. Around this time is when I met my fiancé. ( We are due to marry next year ) My fiancé has taken care of my son for the past year & a half & we are interested in not only changing my sons last name, but seeing what steps would need to be taken for him to legally adopt my son. My sons biological father denies (now he does) that my son is his, & has been gone another year from my child's life. His name is NOT on the birth certificate, I do not get child support from him, & I applied but nothing has come of it yet. I only receive medical help from the state, nothing else. I work & my fiancé is finishing college. So my questions are:

1. What steps do I need to take to change my sons last name to my finances?
2. My fiancé is interested in adopting mybson, what steps need to be taken there?
3. Can my sons biological fathers rights be terminated for abandonment?
4. Do I need my sons biological fathers approval or notification of changing my sons last name?