Howdy from NY.
I have had my home broken into twice. Once, everyone was at work and the guy took his time picking out what he wanted and even fixed himself lunch. The other time was while we were sleeping. He took my briefcase and my wife's purse and we never heard a thing.
Anything is better than nothing in terms of ammo. My opinion is that if it will put a hole in a bad guy, its good enough for me. I think any other discussion about expansion, penitration and the like is beyond what I have to concern myself about.
If you're new to guns and shooting, you might want to take a safety class. You don't want to cause harm to your self or your loved ones when your intent is to help. Also, get lots of practice at the range. A paper target is hard enough to hit at the range, and its not attacking or trying to kill you.
I reload and use a Lee Pro1000. Using locally purchased consumables (not in bulk) it cuts the cost to about 1/3 the cost of factory ammo. I usually go through 200-300 rounds of 9mm a week, so for me it makes sense financially to reload.
I hope this helps.