1) There is plentiful space for the stadium AND parking lots at the Santa Clara location.
2) The stadium will have a Santa Clara VTA light rail station right next to it, which means it's easily reachable from almost anybody with acces to Santa Clara County's light rail system. It should be noted the light rail line from the stadium site goes directly west into Mountain View, where you can connect with Caltrain commuter rail up to San Francisco.