Okay, things have gotten much better.
I wish I had better understood the upgrade system. I thought that since the PC's damage counter said 10 pts. that meant that I needed 10 nodes in order to upgrade. Needless to say, once I realized my mistake, I've now upgraded my damage twice, and my stasis energy once. I've almost upgraded my suit's health as well. I'm also finding a lot of ammo for other guns, but since I'm just going to stick with the PC, I'll just sell it all and get a ton of credits.
About 3 rooms after I started, I found enough ammo to keep me going. What really helped was to use 3 shots to take out one leg, then to stasis the necro on the ground so I could have enough time to stomp them to death. But 2 enemies are really making life tough:
1) Those bat thingies (I think they're called Infectors). THEY WON'T DIE! It takes almost 20 shots to put them down. I've tried using stasis and stomping it to death, but there isn't enough time! It wakes up before I can kill it, and it removes a TON of health if it latches on to me.
2) The tiny bug enemies. I can only seem to kill them one at a time with the PC, and that wastes far too much ammo. But if they latch onto me, I lose lots of health AGAIN!