If I attach Memory Berry to Mareep, evolve it to Ampharos, then attack with "Static Electricity", would I search my deck for energies based on the number of Mareep or the number of Ampharos in play?

In the latter part of the Static Electricity attack Where the English card says "attach them to Mareep", the Japanese card actually says "attach them to this Pokemon". So, you would count the number of Mareep in play and attach that many Lightning energy to Ampharos.

Relevant cards