Question about ENDOthermic and EXOthermic reactions?

Any reaction needs something to get it started; after that we describe whether it takes in or gives off energy using the words endothermic and exothermic. Your reasoning is correct; you have an exothermic reaction. An atomic explosion would be another example; it takes a little energy to start (specifically, kinetic energy bringing two pieces of fissionable material together forceably) and then it releases a lot of energy.