My son was similar at that age. He started at a part-time, private, play based preschool at age three. In our experience, preschool is tough for a really smart kid. My very verbal kid was fascinated with Rube Goldberg machines at the time and loved reading How Things Work. I remember his preschool teacher telling me that he had tried to explain how the internal combustion engine worked (in great detail) to his classmates. On another occasion he asked a class mate over for a play date and suggested they tune the radio between stations and listen to the radio waves created by the big bang together. These comments were amusing to the teachers but made it very difficult to make friends. When he was four my son's preschool teachers approached us and said he was experiencing difficulty focusing on games the other kids were playing, that he didn't know how play with groups of children and that he talked incessantly about chemistry. We had him assessed to see if he had ASD or something else and that's how we learned that he was gifted. The psychologist told us that his main problem was a lack of peers at school. My son started a social skills playgroup and has met several other gifted kids. With them he doesn't seem to have any social skill issues.
This is a very long winded way of saying that preschool may not be the answer. In fact, it may be a very difficult period for your son. If I were you, I'd look for a program that is a few hours a week so he gets time with other kids and can practice social skills. I'd make an effort to find other gifted kids and spend time with them and their families. You won't believe how your kid will connect with them.
I'd spend most of your time just following your son's interests. My son loves spending time in nature so we spend time outside almost every day. We also read stacks of books on whatever he is interested in at the time. I talk to him like an adult and read things that are probably way over his comprehension level but he never complains or loses interest and I often realize hours later when he makes a comment that he understood more than I would expect.
I should add that we never try to teach my son specific things- we just follow his interests. For example, my husband is a mathematician and people always ask if we teach my son math. We don't. But we talk about it a lot and answer questions he has. He has intuitively grasped/taught himself addition, subtraction and multiplication. He understood fractions after I spent five minutes explaining them during baking. He read something about exponents and just understood it. Your kid will probably just absorb things, too. He'll probably need help with other things like relating to his peers and dealing with his intensities. A good preschool program can help with this but it need not be full time.
I think my son enjoys preschool but he is really happy spending a lot of time at home, too. He just turned five and while his friends at school are into blocks and Star Wars, at home we do science experiments and he can tinker and read stuff that he's interested in and have space to be himself. My son is an introvert so this may be one reason he likes to spend lots of time at home, too.
