More than I thought we'd tell, that's for sure! My parents know and a few friends. And apparently when I was a little tipsy on New Years Eve I told my brother, his gf, my cousin and another friend....I only remember telling my brother, oops lol.
This is just some advice from an "older" trying to conceive. My SO and I are TTC and we are not telling anyone until it actually happens. In fact, we plan to get pregnant and wait a bit to make sure everything is ok. Then the first people we plan to tell are our 3 teenage daughters---together---so we can get the drama out of the way all at once. Other than that then both sides of the family.
What is important is that the two of you are happy with each other and your decisions before you let the rest of the world in.