Hey there. To point you in the right direction, I believe the toolbox plugin will help you. There is an element called expression which can accomplish a variety of mathematic equations and spit out a value. As far as the dates, you can use any date and +months to achieve 6 different dates. Date1+(months):1 and date2+(months):2 .
You can also use more than one expression together. Expression1 value + Expression2 value. as well as conditions to change the formula if needed.