Festivities for the Firestone Grand Prix of St. Petersburg begin today in downtown and culminate with Sunday’s IndyCar Series season opener at the 1.8-mile, 14-turn street course. Here’s what you need to know about this year’s version of one of the area’s biggest annual sporting events. It’s bigger than usual The first turn will have more cars vying for space than ever this year. [ IVY CEBALLO | Times (2021) ] The field for the headlining IndyCar Series is expected to feature 27 cars. That’s the most in Grand Prix history (there were 26 entrants last year and in 2012). The event has also been able to resume the Thursday night 5K…