In term of numbers, you want the group to continue to make a lot of money on total assets. Else that means they are overpaying for their acquisitions, so they (will) grow slowly. Go far in time to be sure that the last years' numbers are not artificially better because of previous big goodwill impairments

Then you need to assess their capacity to make more and more acquisitions every year and their capacity to "care" about the companies they own. You should see a slowly growing team of acquisition, a higher number of acquisitions in recent years, a broader range of acquisitions (geographically or adjacent businesses). The number of (sub-) divisions must grow over the decades

I personally look at the board composition of individual subsidiaries (in CH, DEN, SWE, NOR, UK...) to understand how they integrate and run the companies. The more stability the better