What is the minimum amount that a spouse can legally leave their spouse in a trust (in case of death)?

in the state of Florida. He has one 17 year old daughter and is leaving me "the legal minimum allowable", plus is purchasing a life insurance policy in my name. I just want to know, what is the legal minimum.

Legally, since it has to be something since he'd be leaving something, then it would be a penny. The costs of leaving it in trust would be considerably more than that, but legally that is the minimum he could leave. If he did that, then he'd have to leave the fees to keep it in trust, too.

If something were to happen to him before she turned 18, then she would get Social Security until the age of 18, or 21 if she goes to college. He doesn't, by law, have to leave her anything as far as I know. I am a native Floridian and have had relatives die with underage children. They were not left anything and neither were the ex spouses.

See an attorney and get expert advice. You can get short, initial consultation free or cheaply.
Many states won't let you disinherit your spouse, UNLESS they sign off on it, but you can disinherit your children.

zero

If you are CURRENTLY his spouse, he cannot disinherit you without a pre-existing premarital agreement. Therefore, if he leaves you nothing or $1 or other such, the Probate court will invalidate the will and proceed as if his estate were intestate (without a will).

If he is not currently your spouse he doesn't have to leave you a penny.

If you two are still married, half (50%) of the shared possessions are yours by law, fight for it. BUT, with *his* half (50%) he can do whatever he wants and leave it to whomever he wants, no law can force him to leave anything to you. Just make sure that he is not counting on your 50%, he has nothing on it. Regarding the life insurance on your name, go to a lawyer and ask for a "Sworn Statement" clearly stating about the life insurance, the fact that you do not agree with it, the name of the company issuing the policy,...make sure you state everything about it. Ask the lawer to write the insurance company a letter regarding that you didn't authorize the policy and that you want the policy to be annuled. Usually the insurance agencies dont like to get involved in such litigations.

depends on the state. In Washington and California, he has to leave half of his estate to his wife unless she agrees in writing. 401K's , Life Insurance, IRA's all have to be left to a spouse unless released in writing.
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It varies greatly by state

It depends on what law you are trying to satisfy. If you are setting up a trust to avoid the payment of estate taxes, the amount left to the spouse is usually the minimum amount needed to achieve the greatest tax savings.

If you are trying to set up a trust in a second marriage where the parties want all of the pre-marital property to go their kids and not the second spouse, you still have to deal with the assets acquired during the marriage--that might be what he means by "legal minimum".

The best way for you know exactly what he is talking about is to take a copy of the trust and any pre or post nuptial agreements to a lawyer and have them reviewed for you.