Question

1. He likes helping poor people.
2. It is good that he likes helping poor people.
3. I think it good that he likes helping poor people.
3-1. I think it good for him to help poor people.
3-2. I think it good to help poor people.
(Are the sentences all grammatical? I think as #1 and #2 are grammatical, the other sentences can be grammatical. Is that right?)

4. I believe it good that he likes helping poor people.
5. I feel it good that he likes helping poor people.
6. I consider it good that he likes helping poor people.
7. I find it good that he likes helping poor people.
8. I suppose it good that he likes helping poor people.
(I substituted other verbs for good. Are all the sentences grammatical?)

Answer 1

1, 2, 6, and 7 are fine.

If you change "it" to "it's" in the rest, those sentences will be fine, too.