I suppose = 見受ける ("I guess" can be used in the same way)
I suppose I should go to bed earlier, since I was late to work yesterday.
I think can mean 思う or 考える
I think that you are nice.
I am thinking about what to do tomorrow.
I feel can mean 思う (just like "I think") or 感じる
I feel happy today.
Sorry if my translations are strange,
Hopefully this explained it!