There have been two generations of the Mazda5. The first lasted from 1999 until 2005, with the second being produced since 2006.
The first generation Mazda5's were all 4 door minivans with seating for 5 or 7 passengers, depending on if it included the optional 3rd row. The only engine option was the gasoline I4 in the US, while other markets got a choice of a gas or diesel I4.
The second generation Mazda5 seats 6 people and is considered a much improved van over its predecessor. The engine is still an I4, but there are choices that range from 1.8 liters to 2.3 liters.
Transmission options on the newer Mazda5 include a 5 speed manual and 4 speed automatic. There was a recall related to the automatic transmission. If the driver leaves it in sport mode, which essentially allows it to work like a manual transmission, and drives it without shifting like it was a normal automatic, the excessive heat build up could cause damage to the exhaust system. Driving the car this way would be like leaving it in 2nd gear at all times and at all speeds. Only 2,700 vehicles were a part of this recall.
These cars are out there on the used car market. You should expect to pay a premium for the 2nd generation models, not just because they are newer but also because they are much better. Try looking on eBay for some great deals.