I have heard that the excessive flash at night is not nearly as bad as you might think, but you should probably just find a low-light (or dark, if possible) place to shoot a few rounds of whatever ammunition you intend to carry and see if it bothers you. But the ports could cause some burnage if you had to fire from an unorthodox position, like rright out of the holster.
.40 is a fine caliber for defense, it's basically a 9mm, but more of it.
PS- I have the 27, my first Glock, and I love it. Never liked Glocks or the idea of Glocks until I got one, now I am planning on more. Be careful.