Is this game like the old gran turismo where you start off with older cars, win races the can modify and buy other cars?
Not quite. You start off with a lot of sports-car stuff and branch out from there. It's not strictly a bottom-to-top progression, though things like F1 cars tend to not show up until later championships, just because they're more squirrelly. Upgrades and modifications are there for everything, but it's more about customization to taste, sneaking a car you like into a different class, or min-maxing performance in a performance bracket.