Hi Ann,
In a way, Gifted is as gifted does. So if your preschool will keep him with kids he enjoys and see to be similar in ways that they play overall, you are doing the best kind of testing there is.
Is your son just developing early, and the gulf going to shrink? Is the gulf going to accelerate and become even greater, even faster? Who knows? Just worry about meeting his needs now. When the other parents complain, get all misty eyed, and say: "Isn't it beautiful how each one develops in their own natural timetable, like flowers! What a miracle!"
After youve said it for the 75th time, everyone will relax and start to feel better.
Yes, allow him toys, books, and friends who seem to fit him, and don't worry too much about what it says on the box. You will have to protect him from material that he isn't emotionally ready for, as best you can.
Don't give up your parental athority, even if he is smarter than you - you have wisdom! Recognise his need for intellectual stimulation so that he can develop the rest of himself as well, and not be locked in a battle to merely survive.
Try to figure out if you can set up your financial life so that if you 'have' to homeschool him from time to time, you can afford it. Other than that, read books and hang out so you don't get isolated. I like Ruf's Losing Our Minds: Gifted Children left behind.
Love and More Love,
Grinity
