Combat: One would select Variation 1 and play whatever playing field that variation is set to and hope for a good time.
Combat: Three different playing fields in Tank, two in Clouds. Seven variations of play per each of four categories. Ehh.. I'm not sure exactly how to calculate the different gameplay scenarios possible, so I'm not going to try. Significantly less.
Not sure what you mean by seven variations per category. It's best to think in terms of variation number and group number. By group I mean a set of four playfields, one from each category. Combat has one group, and Redux has seven. With 27 variations and 7 groups, there are 189 scenarios.
Take a look at the variation table below. Each variation is set to a category, as you can see in the rightmost columns. When you choose a variation, you can then choose a group, and the playfield from the appropriate category will be selected.