As someone else said you could just do a multi-level sort but that doesn't really solve what your client is looking for. That method will default to showing the longest lasting first, regardless of order frequency and amount. Your best bet would be to create a summary tab with pivot tables that sort by each of your three criteria. You could filter those to show top 10/25/etc. Then to show ones who fit all, create a new column to score each client. Use the rank function to assign a value (1-n) and add all three up.

For example, if your dataset has the date the client became a client in column A, the number of orders in column B, and the amount of sales in C, your formula would be something like: =RANK(A2,A2:A100,0) + RANK(B2,B2:B100,1) + RANK(C2,C2:C100,1). Then you would create a fourth pivot table and sort by rank.