What are the maine laws if my mom died without a will?

Retain a lawyer to help you. You write that your mother and step father lived 6 months in FL and 6 months in ME. Legally, one of those states had to be their primary residence--*everyone* must have primary residence. The intestate succession law of the state of their primary residence will apply, and that may change the answers to your questions; a lawyer can help determine which state was their primary residence, and also deal with other sticky issuesl, like the interplay of the FL "homestead" law, which protects someone's residence from creditors--including potentially other heirs. 
The above said, since when there is a spouse and children not with that spouse, *both* ME and FL give the children (you) a share of the estate, you should get a portion of the estate. Assuming there is value in the estate (e.g. the homes are not underwater on their loans), you should therefore get *something*. But there is not enough information to tell you how much you might get, since in addition to determining which state's law applies, there are other factual issues that could *drastically* change the outcome. For example: if any bank or brokerage accounts were held jointly by the two of them, they are NOT part of her estate; rather, on your mother's death, they automatically became the property of the surviving joint account holder (your step father). Similarly, any account solely in her name but held by her as "transfer on death" or "payable on death" would not be part of her estate, but rather would go on her death to the payee or transferee listed on the account.
Therefore, depending on what she owned, how she owned it, any liens or mortgages, and the value of FL real estate which may be affected by the homestead law, you could range from being owed more than half her estate (e.g. if accounts were POD or TOD to you) to roughly half to well less than half (if the FL real estate is protected from going to you by the homestead laws and any accounts were joint with him).
This is a complex situation; you need a lawyer to help you.
As to your other questions: 
1) There is no central registry for wills unless your mother voluntarily (it was not required) filed it in one of the counties in which she lived. You can check with the probate courts in those counties; otherwise, unless you stumble on it or speak to someone with knowledge, you may never know if there was a will or not. Try calling any lawyers or accountants she had, and any lifelong or old friends of hers you know of.
2) Similarly, there is no central site for insurance policies. Try contacting all the major insures with your mother's information.