cleaning cast iron cookware

Now that I have just retired, I want to begin to use my cast iron cookware that I have had for many years..I have never used them....much of them I picked up in junk stores, I cant remember when. I have a number of skillets, griddles, and dutch ovens, mostly Wagner. They look in very good shape with a good black finish...some rust, not much. My question is do I need to re-season or can I get by with a simple cleaning as in boil some water in the skillet/dutch oven, dry, and top off with a proper oil???...The reason I ask is, I have no idea what was cooked in or ever resided in these old cast iron pieces over the many years I'm sure they have been around. . Don't know if anything that might have been harmful to the human body was ever put in them. Should I worry about that??..What's the best process to get started. I can't wait to cook some cornbread and biscuits like my grandmother used to do over her old wood cook stove in south Georgia.

If they have a good finish as you say, I would just use them and oil when done. If you are worried about it, put them in a fire, burn everything off, and re-season. As always, you will have to make the call.

Oh boy did you come to the right place!

This is Jocelyn Campbell, "one of the worlds foremost experts on how to deal with cast iron skillets".
She is also a gracious contributor in these forums.
You can take your cookware back to zero and start over completely. This will remove all doubt about what's gone into your goods.
You can start from scratch and build a new season on them.

This is a 9 page thread here in the forums: using a cast iron skillet ain't so hard!
Lots of insight to be found.

If you only want to clean one you can use a torch. The easiest way to clean more is to build a fire and put them in it and let everything burn off. VERY IMPORTANT is to do this when the temperatures outside are hot. The iron pots have to cool gradually; do not run water over them when hot. If the temperature is cold and they cool too quickly they will crack. After they cool down wipe clean and rub with oil.