The location for the Ajijic market is in the linked website. The Ajijic tianguis is on wednesdays, Chapala on Mondays, Jocotepec on Thursdays (this is the closest town to the hotel, and happens 2 days before the wedding). The address is Zaragoza 22, El Panteón, 45806 Jocotepec, Jal., Mexico.
They all occur from around 8 am - 2 pm. Going earliest is the best.
Ajijic, Jocotepec, and Chapala all boast Malecons, which are piers along the lake. Ajijic is my home town one. They usually come alive in the late afternoon, early evening with children playing and local vendors selling fruit and everyone coming to congregate and walk along the lake. Early mornings it is a popular exercising and morning walk spot. Great place to watch the sunset.
Like the Malecons, all the towns boast a plaza. This is another place for cultural congregation also usually around late afternoon, early evening. The Ajijic plaza is a short walk up the street from the malecon. There are restaurants and people watching, and it is all situated around the main church in the town.
Local horse back riding can be found in the La Floresta area. The best way to do it is to just show up sometime between 10 AM and 3 PM and ask for horse back riding tour.
There are many hiking trails around the area. They are all free except the Tepalo hike which requires a small donation in pesos to help upkeep the trail.