I have been lucky enough through many sacrifices to be a stay at home mom. I have a son who will be 3 in January, and though he was late talking, he can already complete his alphabet on his own, count to 20, though 14-19 pretty much all sound the same, and he can count backwards from 5-1. Also, he is now counting to 10 in spanish, which I didn't realize he could do until day before yesterday. I spend quite a bit of time counting with him, and practicing other school related topics... alphabet, counting, spelling his name, colors, etc.
My question then is: When I enroll him in preschool, is it likely that the teachers will ostrocise him for being "smart", or will they look at it as a tool for other children to learn from?
I know what I would do, but a friend of mine had a problem when entering her daughter into preschool, with the teachers completely ignoring, and or being mean (not physically) to her because of her intelligence.
Other question... perhaps I should keep him home; circumstances willing, until kindergarten... what's my best course of action?

If the teachers are doing their job appropriately, they would be encouraging growth in all children, regardless of where they are.

In your son's case, he may end up going over some of the things he already knows, but that won't hurt him in the least. Repetition is often very good for young children to reinforce the concepts and learning these things through play, stories, activities, songs, etc. would be ideal. Hopefully they won't be doing actual "seatwork" at that age.

A bigger issue with preschool is simply the socialization aspect. Kids will pick up on the academics just from their interactions, but to prepare even more for a formal education, the social interaction with others is going to be just as important, if not more so.

Thank you for your reassurance.

As DoulaLC mentioned, the social aspect is really a benefit of preschool. Why not do a part-time preschool if you can continue to stay at home? That way you can continue to be the main stay in your child's rearing but he can also learn the social interactions which are so, so important for children at that age. There really is a lot to be said for a balanced environment at that age. Look for a preschool that has a balance of creative play and structure... it will serve your son well in the future.