If this goes through to court, you would need to use the guidlines as they are in the child support calculator on the home site. Child support is based on the parents incomes, insurance and daycare fees paid out and the number of overnights the child spends with each parent. The “floor” you are referring to would be what your monthly salary is, no negotiating. The only way to deviate from those guidlines is for you and your ex to agree on an amount and to sign an agreement. Be aware though that it can be brought to court at any time in the future, and your salary would be verified and used then.
The best scenario for the child is basically what you two are doing now, sharing time and working out the details between you. It is more emotional, stressful, and expensive to go to court for custody or child support. Run the calculator and see what you would be paying if this went to court. If you are dividing the time equally between you then my suggestion is you pay a reasonable amount of child support if you make considerably more and split everything else. You pay for stuff during your time, and she pays during her time. Medical bills, pay out half…school supplies (when that is an issue), pay half.
You must keep in mind that if you are going to have joint legal and physical custody you will need to work together to raise your child separately.
If custody is not decided by the court or an agreement then each parent has the right to 100% custody of the child. If she is taking the child on a vacation, you may get her to agree to contact you if plans change.
You can file for absolute divorce after one year and one day separation. Custody and child support can be filed for at any time and does not have to be decided prior to absolute divorce. Equitable distribution and alimony must be at least filed claim prior to absolute divorce. There are do-it-yourself divorce kits at some of the local office supply stores and there are also some forms on this web site.