One thing to never do is put them out in a container in the sun- even if it seems cool enough, heat builds up & can kill. Years ago I tried to help someone's pet snake who did this, but it was too late- the snake died from heat stroke. The owner meant well but didn't know any better- they left him out for about 30 minutes in an aquarium with a screen top, thinking it would be okay. It wasn't.
As for whether to hold your snake or allow on the grass, there's plenty of disagreement there: I always hold mine- only. Where I live, there's too many risks in the grass, & good herp vets nearby don't exist, so I don't take that chance. Your snake can pick up all sorts of parasites (chiggers, ticks, worms, etc) & pathogens left behind by other animals (even birds & local lizards), so I don't chance it. (FYI, even YOU can get "worms" by going barefoot.)
Also, you want to be sure that the lawn wasn't treated with any kind of pesticides or other chemicals- your snake can absorb them thru their skin. I know it's tempting to let them crawl in the grass, & they absolutely love it too- many photos on this site of members doing just that. Not me. Also- it's hard to see small holes in the ground that are obscured by grass- but your snake WILL find them, just like they find their way into couch cushions & such. Be careful...snakes won't come when you call them.
You ask great questions! Sorry about my long-winded answers-
