Your sentences are perfectly good.
What's the difference between 'feeling' and 'feelings'?
Are my understandings that 'feeling' talking about how one feels from the environment and 'feelings is reflecting one's emotions correct?
May I ask the differences between 'feeling' and 'feelings'?
1. It was such a nice feeling to be home again.
2. She has deep feelings about what her father said.
3. She expressed warm feelings toward her mum.
Is 'feeling' talking about how one feels from the environment and 'feelings is reflecting one's emotions?
Each of your three examples uses "feeling(s)" as a count noun, where "feeling" is singular and is preceded by "a," and "feelings" is plural.[strike]Are[/strike] Is my [strike]understandings[/strike] understanding that 'feeling' is talking about how one feels from the environment and 'feelings' [strike]is reflecting[/strike] reflects one's emotions correct?
Each of your three examples uses "feeling(s)" as a count noun, where "feeling" is singular and is preceded by "a," and "feelings" is plural.
In its countable sense, "feeling" relates to emotions or sensations. In its noncount sense, "feeling" means "sensitivity." Examples of "feeling" (noncount):
4. He plays the piece with feeling.
5. He has no feeling in his right arm.
Since 4 and 5 are [no article] examples of non count 'feeling', would you mind giving [no article] examples of countable 'feeling'?
Yes to both questions. I would think twice, and then think again, before disagreeing with any part of the OED family.