Keep track of how many nights you have with daughter. Courts count nights, not days when dividing custody. You have two choices:
1. Go to family court now for Joint
legal custody (school and medical choices) AND Joint Physical custody (50/50)
or
2. File in Supreme divorce court and file divorce which will include the custody
Choice 1 will go faster and then you can take those papers and incorporate them into your divorce for an easier divorce. It also deals with visitation/
parenting plan right away, while a divorce can take a year or more if you have to go to trial. She may play hard ball and try to force you out of house. Stay in house, unless a court tells you have to leave. If you have to, move into another room.
Choice 2- gets your divorce rolling and dealing with money/house issues.
What you can be doing:
-Close all joint accounts, open accounts in each of your name, see if you agree to split any savings you have, put in separate accounts. Credit cards, take names off each other cards. House bills have in your name if you can pay them and want house.
-Do not offer ANYTHING right now to her in writing. Can she start looking for housing now? Even if she takes money from joint account to pay for rent for first 2-3 months. Courts usually want you to buy her out of the house not make an agreement to pay housing. What if you lose your job down the road? Maybe you can refi the house in your name only taking some money to pay her off. Can even try to start that process now or wait for a
court order so the banks are more willing to do it.
-Child needs to know that she will have two house/beds. If mom, moves out, it should be in same school district as you so you can keep 50/50 custody once school starts. As soon as mom moves out, child should be sleeping at mom's. Nanny can go there. Make sure you have temporary written agreement first as she can keep daughter.
-School- as long as you are near her, 50/50 can be done. Since you make a lot more than mom,
child support can be given to mom so that child living conditions are comparable to yours.
-Money- In addition to child support (you can look up child support calculators for your state to see how much), you will split by percentages of your salary compared to hers for : medical costs, dental, activities, education, daycare in most states. My state child support is 17% of income for standard visitation....
-Child needs both parents no matter what mom did outside the marriage. As long as she can feed, clothes and shelter child she is a fit parent in family court. You will need to come up with a fair holiday and vacation schedule. Get a local school calendar (online) and there are a lot of long holiday weekends to put into papers along with birthdays for you and child , Halloween, and fathers day. There are holiday schedules on this site and online.
SO to answer your question, probably hire a lawyer (interview a few) and find one that will really fight for 50/50 not matter what. Tell them you will not agree to something in hallway that you are willing to go to trial. Some lawyers just like to go each month to hearings and just want you to agree. Then decide where you should file. Mom will get a lawyer too who will be telling her what to do and not do so it will get ugly. There is nothing right now stopping her legally from moving into a house and taking daughter with her right now. You are both her parents and no court order so go talk to some lawyers and see what options you have. Ask questions on here, many here know about 50/50 custody plans and different ways of doing it. Good luck!