If my neighbor that I am friends with in real life wants to be my friend online, is that OK? short answer

Yes.

What do I do if someone wants to be my friend, and I don’t know who the person is? short answer

It is recommended that you do not accept the friend request unless you can verify who the person is.

Yes, it is generally okay for your neighbor, who is your friend in real life, to also be your friend online.