Thanks for reaching out to us.
>> I need to derive a list of top 20 customers based on the actual sales (Fact Table 1), and then return different numbers for those twenty customers from multiple fact tables
you can first filter out the top 20 customers in Power Query by filtering the sales of each customer, then use Merge.
For example, to filter top 3 sales first,
Finally expand table,
Community Support Team _Tang
If this post helps, please consider Accept it as the solution to help the other members find it more quickly.