I have an ex who has been a nightmare from hell. We have a child together and for about 6 months everything worked out well. She is now seeking to obtain the child support through the state of IL and the question I have to ask is this?

First let me set somewhat of a senario. My ex-girlfriend and I (never married) have been broken up for about 6 months and we have agreed verbally on me paying the car, insurance, cell bill, and depositing money into an account we opened together to document support payments. Now 6 months later, she is telling me that she is going to use the state of IL to collect full payments and have them automatically withdrawn from my payroll. Now here are my questions.

1. Is it necessary for support payments to be automatically withdrawn from my payroll if I am willing to pay voluntarily?
2. Now that she is threatening to sue for this child support, is it wise to stop payment of any bills I now pay for her and take back my car? What my thing was is that I would provide them with a vehicle and assume financial responsibility, therefore those payments would essentially be part of the child support payment. So do I stop paying, take the car back, and make it so that she just receives the full support payment, and no other payments.
3. What is the percentage of my income that I must pay for child support? Last when I spoke with a lawyer, he told me 20% for IL. She is telling me that her lawyer is saying 33% for abandonment reasoning, which I have no idea where she gets that from. Now when we broke up, it was a mutual thing and I left her mothers house, where I lived for 3 years.
4. What are my rights as a father about her traveling with my son out of the state? She made me aware of it, but do I really have any say in it?

Now I understand that any posts or responses to this question is NOT true legal advice. I have met with a lawyer and we have spoke about everything mentioned, but I am looking for more views and opinions from others who are knowledgeable in this area of law. Please any advice or statements will be researched and only intrigue my sense of curiousity as this law process proceeds. Any info is good info, but that doesn't mean its true.

Thanks much.
-MrMike