Dear Dana, I live in San Miguel de Allende which would be too far for your husband to travel to on a daily basis. I know several German speaking people here, as well as 2 doctors that I wouldn't use. There's 2 international schools and a Waldorf and Montessori school.
However, rentals and real estate have gotten more and more expensive over the last few years. Tourists flock here every weekend making the Centro very overcrowded. Traffic jams are what we deal with every weekend and holiday. That said, it's a lively fun place with many things to do and see. All that I know about Irapuato is that it is the strawberry capitol. León is convenient and has an Airport and a centro with many stores and restaurants. I would choose Quretaro myself because it's a growing city with many things to offer: schools, new housing, nice neighborhoods, good shopping, and safe. I am retired and don't have a car and many times I miss the benefits of a city over a small town. I'm sure you'll want to eat good German or Slovak food but it's impossible to find unless you have it shipped in, which is expensive. I go to Costco or Sam's Club to buy sausages or wursts or salamis in Queretaro. My late husband was Czech and he couldn't live without those foods.
He was an engineer for Siemens and did international service, but wouldn't live anywhere that didn't have good hygiene and European food. I recommend that you visit León and Irapuato first before making any decisions. Good luck to you. Ronnie Treitler Mudrakova