1. For a Shaiva, Shiva is Brahman. For a Shakta, the Mother Goddess is the creatrix. There are other views also.
2. Again Shaivas and Shaktas believe differently about Supreme Manifestation.
3. Oh yes, Vsihnu is a (Supernatural being) and so are Shiva and the Mother Goddess.
Here again, there are different views.
1. Followers of Sri Madhvacharya (Dvaita philosophy) say Vishnu/Krishna is separate from us.
2. Followers of Sri Ramanujacharya (Vishishta Advaita) say Vishnu is the same as you and me but there is a qualified difference.
3. Followers of Chaitanya Mahaprabhu (Hare-Krishnas) say Vishnu/Krishna is the same as you and me but the similarity and difference are indescribable (Achintya Bheda Abheda Advaita).
4. Followers of Sri Nimbarkacharya (Dvaita Advaita) say that though Vishnu is the same as you and me, but the difference is that Vishnu is independent where as we are dependent on Vishnu/Krishna.
5. Followers of Sri Vallabhacharya (Shuddha Advaita) say that Vishnu/Krishna is the same as you and me. But that we are in ignorance, and the ignorance can be removed by only grace of God.
Advaita of Sri Sankaracharya says there is only one, call him by any name, know him in any form. And that is not the end of sects in Hinduism who all live side-by-side with each other. There may be differences between the views of two members of one family and it would not surprise us.
Basically, Hinduism gives a whole lot of freedom to formulate one's views (it is not that there are no limits but the expanse is very large). Others may not agree with one's views but they are expected to respect a person's freedom in the matter of beliefs. We are guided by the saying 'Eko sad, Vipra bahudha vadanti' (The truth is one, but noble people describe it variously).
I think, once you accept this, Hinduism will be easier to understand.