Every now and then items appear in the stone circle, so be sure to check there when making your rounds.

Hold your finger on the item until it turns green. Then you can move it around and also turn it around.

You don't do anything. Nothing happens.

Things will appear there now and then so check

I plant them all. Haven't kept track of what I put best other though.

Keep talking to them whenever you see them. Try to find the things they ask for. Sometimes they get mad at each other or are feeling lonely...talk to them! I gave one an orange when it said she had a cold.

I plant them near one another in kind of a circle pattern. I've gotten four new plants so far....a cactus looking thing, a blue rose, white flowers, blue flowers

I usually only find them at night...on the beach side or in the woods in town

As you roam around, keep note of where you find certain bugs. They tend to appear in the same place every day. Some only appear at night. I've found some new bugs (like the termite) by zooming in as large as it will zoom and then walk around.

I've tested it several times. Selling food to the store DOES count towards food. I harvested all my food and my food supply went down. Then I sold it to the store and the supply went back up.

Put fertilizer on it and then water it.

I don't have it quite figured out but putting fertilizer on some plants does create a new plant. Sometimes you'll see what looks like just a dirt circle with a stick in it. Watering it does no good. Put fertilizer on it and it will turn green. You'll get a new kind of plant that way.

Selling food to the store does count towards food source. Leaving it sitting in your inventory does not.