You have three questions and the answer to all three is yes: 1. you need an attorney. 2. If what you are saying is true, you have a good chance of getting custody but she might receive visitation rights. 3. A judge can rule the way he/she decides so there is a chance the bio mom might get custody, which brings me back to the reason why #1 is yes.
I agree with attorney Zachary, and add that custody is now called "legal decision making." Also, the mother is likely to be awarded "parenting time", not "visitation."
My understanding is that there are no orders in place currently. You should be prepared for a judge to award joint legal decision making, as courts (in general) prefer that both parents be involved in making the major decisions for a child. With that being said, there are certainly reasons why a judge may award you sole legal decision making. There may also be reasons why a judge would limit her parenting time.
You should consult with an experienced family law attorney so that you may provide them with a more complete picture of the mother's history and yours, and the needs of your son, so that you may obtain legal advice that is specific to your case.
Ultimately it is a personal decision as to whether to hire an attorney. Attorneys can take a lot of burden from their clients, as we are trained in moving matters through the court system, dealing with the court filings, proper responses to be filed, dealing with opposing counsel or party, and most importantly, preparing for and advocating for our clients at a trial/evidentiary hearing.
The information provided is general in nature and does not create an attorney-client relationship.