My advice is don't stop at 3. You know that old saying, "Two's company, three's a crowd"? Well...it's an old saying because it's true. I had three boys and regretted stopping at three all these years hence....any two of them at home got along, but as soon as the third came back, FIGHT. Didn't matter what combination of two, they seemed to get along just fine...but add the third and it was constant squabbling and it still is, now that they are grown.
My eldest has two girls and are awaiting the third and then they plan to stop...and I keep telling them they are crazy for not having at least one more. Pairs play WAY better than trios.