Complex sentence: First of all, it is necessary to think of the best way to operationalize the variables that will be measured, as well as which statistical methods would be most appropriate to answer the research question.
Split into simpler sentences: First of all, it is necessary to think of the best way to operationalize the variables that will be measured. Therefore, it is important to consider how the variable (s) will be measured, as well as which methods would be most appropriate to answer the research question.