We are flying from MCI to Amsterdam. Several choices of flights with plane changes in various cities, What should I allow for comfortable time between flights? Will we go through customs in Kansas City or whichever airport our flight to Amsterdam leaves from?

There is no customs when leaving the states.

How long you need on the ground varies significantly depending on the airport.

Customs deals with the transport of good into a country - so most places, you will go through customs when you arrive in a country (or cooperative zone, like the Schengen Zone in Europe).

Immigration deals with the transport of people into a country - and similar to customs, you will go through immigration upon entry into a country.

There aren't any exit controls when leaving the US.

So, if you connect through a US airport, and your point of entry in Europe is Amsterdam, you will go through both customs and immigration there. If you connect in Europe, in the Schengen Zone specifically, then you will go through immigration and customs at your connecting airport and then your flight onto Amsterdam will be just like a domestic flight within the US.

If you connect in Europe, in the Schengen Zone specifically, then you will go through immigration at your connecting airport and then your flight onto Amsterdam will be just like a domestic flight within the US. You will then go through customs at your final arrival airport.

No matter where you are connecting, allow more time rather than less, especially if the connection is late afternoon or evening. The last thing you want to have happen is for your inbound flight to be delayed for some reason(I.e. weather, mechanical difficulty) and then you miss what is the last flight out of your connecting airport for your destination for that day.

Connecting to your flight to Amsterdam will be about as easy as a domestic flight. Boarding usually starts earlier though.

Ultimately, though, your connection time will vary from airport to airport and from airline to airline. It is hard to give a great estimate, but I would think 2 hours on the outbound should be enough in most instances to enable a comfortable, if not slightly long connection.

2 hours should be plenty but it ultimately depends a lot on the connecting airport and airline.