1. The Chinese are an industrious
people.
2. Chinese people are an industrious people.
3. The Chinese people are an industrious people.
(What does #1 mean, #2 or #3?)
4. The Romans were strong.
5. The Roman were strong.
6. Roman people were strong.
7. The Roman people were strong.
(What is the difference among them? Which one is right, #4 or #5?)
1, 2, and 3 all mean the same thing, yes.
4, 6, and 7 are all correct and mean the same thing.
5 is not correct because "Roman" in this case seems to refer to a singular person, so it needs "was" for its verb.