You have several problems only connected by toilets.
“problem with a stopped up toilet on the second floor. Called a plumber–he didn’t find it. Now
same toilet runs constantly and takes forever to fill”
This is caused by the fill valve and not related to the blockage. You need a new fill valve and a flapper.
“Then the same toilet overflowed. Then I noticed water on the ceiling in the kitchen and I’m hoping it’s related to the toilet problem and not something else.”
Most likely water from the overflowing toilet that staturated the floor around the stool and came through the ceiling.
“I noticed that the powder room toilet (on the first floor)would not flush today.”
Was this caused by backing up or a water supply problem?