I need native speakers'intuition about these sentences

Please check the grammaticality of these sentences again. Can i use BUT and AND in them? I'm very confused about choosing AND and BUT. Clive told me that it's writer's choice. So can i use AND and BUT as i wish. PLease help me to undestand it!!! Thank you very much in advance.

Many people expressed concern, and a few were willing to work.

Few people expressed concern, and some were willing to work.

All people expressed concern, and a few were willing to work.

A few people expressed concern, but all were willing to work.

Not all people expressed concern, and a few were willing to help.

A few people expressed concern, but not all were willing to help.