Questions for an upcoming visit - Internet, Transport, Food, Tennis?

Since your trip is over this is a bit late but I'll offer my suggestions for the benefit of others reading this who have similar questions.

If you are traveling with a group of people you may find that a private car service is cost effective. I've been using San Miguel Drives for 8 years and he has transported up to 6 adults for me. The charge from Leon or Quetetaro including propina (tip) will amount to about $43 each person for four passengers (each direction). The bus may be cheaper but you can't beat the ease, the speed and most important the hour long discussion with a native from San Miguel who speaks excellent English.

Like most any city in the US you just need to research the local cafes, library etc for who offers WiFi. Look for the signs in the windows, host stands etc. Cellular gets easier each visit. When I started traveling to SMA I would have to start an international plan at the onset of each trip. The charges were high, especially if you went over the allowed minutes of your plan. Now my carrier (AT&T) offers free roaming in Mexico. I only had to go online and add the option for $0.00 and I'm good now when ever I visit. Since the construction most of Mexico including SMA is solid masonry you will find reception problems when inside larger buildings with multiple floors...like similar buildings in the states.

Crime? I get disheartened every time I encounter this issue. The US media has done the people of Mexico a huge injustice. There are 33 states in Mexico, 5 of which have issues that should make visitors research just what the crime is about and where to take extra precautions. Yes there is crime in Mexico. Yes there is crime the state of Guanajuato, and yet there is crime in San Miguel. (The crime rate in Austin TX is higher than in SMA by the way.)
There is crime in every corner of the world. Just last week in a suburb of DFW, one of the most affluent towns in the country a woman was gunned down in the middle of the day in the middle of a busy street. Be alert, don't flash your money and stay in groups should you get into a dark street late at night. That advice has to do with being in Dallas, LA, Vegas etc so I guess you might want to take the same advice with you to Mexico. I do have one caveat specific to Mexico. If you are in the drug trade and advancing on rival territory or challenging the police/military you might want to stay home.

I have visited San Miguel 19 times in the last 10 years. Only once did I feel I had a gastro issue and that was the result of eating at a roadside Gordita stand outside of town. They were some of the best I've had and I'll go back. I think the culprit was the fresh squeezed orange juice.

The water is the issue. Your gut is not used to the bacteria etc specific to the area. Drink bottled water or inquire with your waiter if the water is purified. As another responded mentioned you may want to eat in busier restaurants. If you prepare your own food in a rental house be sure you buy some iodine solution and soak your produce. That is the second most common source of the bacteria, unwashed produce or produce washed in the water you are trying to avoid. Have fun dining in SMA, there are wonderful restaurants of all varieties and they take the precautions you need, the last thing they want is a reputation that people get sick after eating there.

As for tennis. The hotel Real de Minas advertises a pair of hard courts. Nearby in the same neighborhood of San Antonio there are two facilities. The Webber facility is a public facility hidden off the street behind a gate, they have 3 clay courts. A block or two away are the pair of clay courts behind the Hotel Posada de La Aldea. I suggest you visit the Webber and Aldea facilities and decide if they meet your needs. They are not resort caliber courts and the Webber are the best of the two. If you want higher caliber courts the golf club Club de Golf Malaquin outside of town has 4 clay courts and can be accessed by non members. I would expect they are better built and maintained courts.