Not joining all 4 families right away is a typical mistake.
Trials are very short and impossible to fail, You get free vehicle and unlock an important game feature that is usefull even if you dont plan to do any more events from that family
Street racing unlocks livery editor
Offroad unlocks photo ops for all 4 families. Most photo ops are fast and easy money boost you can really use in the beginning.
Freestyle unlocks free roam tricks, You start getting followers/xp for doing things like drifting, jumping, flying under bridges or even just speeding in free roam. Daily contracts that require you to do those tricks wont register unless you unlock this feature.
Pro racing unlocks video editor.