It may be that your son is a bit immature in some of his development, though I cannot assert this with certainty based only on what you have noted. Re: his pay with the cars, you needn't worry about that. Re: the need to repeat directions, be sure you obtain his attention (including eye contact) before you issue a direction. Say the direction no more than two times. At the time you issue the direction a second time, do so in the form of an 'ultimatutm' - i.e., Unless you ...., you are going to time out. If he doesn't follow the direction, place him in a time out chair for a few minutes. The clinging behavior is not uncommon in thirty-month olds - while they like to explore and become a bit more autonomous, at the same time this makes them a bit anxious and they need the security of staying close to their parent. Be sure to touch bases with his pediatrician and seek the dosctor's opinion about the status of your son's overall development. And remember that children to not proceed at the same rate in each of the various areas of development - there is always a certain amount of unevenness.
Magic 1, 2, 3.