Mark,
I agree with a lot of the advice given here. I recently purchased an M4 to anchor my home defense plan. It compliments my Glocks and CX4 carbine. But there were many considerations to my many choices of weapons.
I took into consideration my small wife when selecting long guns. The M4 has more recoil than she's comfortable with, so we also went with a Beretta CX4 Storm in 9mm. It holds 15 rounds, a mounted light and she can shoulder fire it without any problems. It is a bit of a compromise as weapons go, but in a good way I think. It has the benefit of an accurate shoulder fired weapon with the lower recoil of a handgun round. The weight also helps absorb recoil, and the sling allows hands free carry if necessary.
For hand guns, she carries a S&W J-frame .38 with CTC laser grips and an internal hammer. It's light, simple and effective. Load, point and shoot. It doesn't get any less confusing than that. So much so, my mother and mother-in-law carry the same pistol.
We did make sure that we each have at least one weapon with a mounted light. I couldn't imagine trying to control my dog while handling a light and a weapon. Also we don't have kids and neighbors so ammo choices aren't as critical. I load what I need to get the job done without worrying about over penetration. It should be a prime consideration though, depending on your situation.
I must say that marksmanship is a lot like golf in one respect. You can practice all day, but if you're using the wrong technique, you'll never become proficient. A competent instructor can help develop your skills in a way you're comfortable with and that work for you. My mom is left eye dominant but right handed. After trying every technique I could think of to help her learn to use her right eye, we came to the conclusion she should shoot left handed. A good instructor will not force you to adapt to their method but help you find something that works for you. Shop around. They're out there.
TH13