1. 感覺 VS 感受
感覺:more related to physical feeling
EX: 你生病一週了,現在感覺如何? (You have been sick for the whole week. How do you feel now?) (asking physical condition)
感受:more related to mental feeling
EX: 聽到那則新聞,你現在感受如何? (After knowing the news, how do you feel now?) (asking mental condition)
And I personally think 感受 is sometimes interchangable with 感覺 but it depends on whom you ask.
(Also to me, I find 感受 more like a written language and so a little more formal).
2. 覺得 - you can use this to express your opinion, usually translated as (I) think or in (my) opinion.
For example, 我覺得你人很好 ( I think you are a good guy; in my opinion, you are a good guy).
EX2: 他覺得我很醜 (He thinks I am ugly.)
Hope this post helps.