Effective January 1, 2009, the Florida minimum wage is $7.21 per hour. Failure to pay at that rate would be a violation of state law. Also, the rate stated in your question does not meet federal minimum wage requirements, currently set at $6.55/hour.
With respect to overtime, generally, any hours worked over 40, subject to limited exceptions, must be paid at a rate one and one half the regular pay rate. The size of the employer is not relevant.
Regarding a change in pay rate, an employer is generally not required keep an employee's pay rate the same, unless there is an employment contract specifiying a particular pay rate.