Ex taking our child to new girlfriend's house overnights. She has a criminal record. Can I legally stop him from doing this?

Get a court order or call DCF if there is some type of emergency. Use of a lawyer is recommended.

A father (whos not seen his child in years) just put open access insurance on my son, Who is to pay this???

Question not clear. Use of a lawyer is recommended. .................

What is a good baseline to allow a absent father see his child? Can I ask for it to start slow? does his gf have to be there?

Cases in which a person has been absent and now wants back in are difficult, start slow, get the court involved. Use of a lawyer is recommended.

Is there any course of action which may give me legal relief?

Move out....

What can I do to get his rights terminated and change my sons last name back to mine at little to no cost as I'm a single mom of

You have to file a petition for termination of parental rights. Use of a lawyer is recommended.

Can I get in trouble for not sending her back to florida

If there is an order in place then you have to comply with the order, until it is changed, you can petition to change the order. Use of a lawyer...

Can I receive any additional income from him, such as lifetime alimony or increased child support?

Please have a lawyer review your documents, as it is not clear whether you have a permanent alimony award. If you do then maybe you can extend it...

A dependency order supersedes a custody order in family court, yes. Use of a lawyer is recommended.

So long as the house is legally established as your Homestead, no. You should however work to straighten out the support arrears. Use of a lawyer...

My husband and I want to take our son to court to establish visitation rights for weekend and some holiday birthdays

Unfortunately you as grandparents have no rights under family law. in FL.