You have to normalize data taken from various sources of various age and complexity. So you really have to understand the data. You also have to really understand the questions.

I've worked with (and on) lots of these tools and projects; the complexity is never in the frontend, it's dominated by getting the data, getting the data right and into the right format.

If all you want in the end is a good looking dashboard on a website then you might as well build it yourself; because of the cost structure that can even cost less than buying one of the BI frontend tools (there's not a lot of difference in development time, the the BI frontenders are more expensive because they are rarer and the licencing is high).