Okay, I'm progressing on my plans to outfit myself...

What should I look for in a headlight? In panniers (I read about balance and steering issues)? Any specific recommendations? My budget is tight...

Headlight depends on what you want to do with it. A too be seen light, or a to see light?

This would depend on your riding speed, road lighting conditions and the route you'll most likely be taking.

Panniers don't have balance and steering issues if they are mounted on the rear on a rack. They might start affecting steering if you have handlebar mounted bags and front panniers.

Operator hit most of the points on lights. You need to consider where you will ride, available street lighting, etc. If you want a light to see with, then you start talking more serious money. You might want to consider a DIY home built light if your budget is tight. You can build some very bight light set-ups for comparatively little money and there are plenty on plans on the web.

I doubt you'll have problems with pannir balance unless you are carrying some incredible weights.

Many DIY lighting systems assume that you want to fabricate a lamp unit and the electronics. You can buy dynamo-style lamps (with mounting bracket) pretty cheaply. You can power these from a dynamo/generator or a battery. I use a rechargeable battery stuffed into a waterbottle, and bought a recharger from an electronics store.
Modern LED battery headlamps seem pretty effective.

For panniers, look for a modern quick-release, locking mounting system not the old fashioned hook and elastic.
Get tough material. A flap is more useful than a zip closure is you need to overload the bag.
You need good stiffening material on the back and base.
Some have lots of compartments, but I prefer on main and one side pocket.
You can use a single pannier quite safely.