The topic is very subjective as is much of our lives.
Jesus, to those Hindus who believe in him, believe him to be just another avatar of Vishnu, while some simply disregard him, some, the son of God, and others, as a mentor albeit, not holy.
1) To achieve Krishna through Christianity is a very silly idea, since Krishna was the name of the body in which Vishnu took part. I would say no, you cannot achieve Krishna through Christianity, however, you can achieve God through Christianity.
Personally, though many people (including myself) regard all religions as equal (refer to Theosophism), Christianity does not offer the depth of practice and spirit that Hinduism gives you. You do not have to look very far to find practical approaches to life and business - the three paths are straightforward and without complicating metaphors (albeit supremely poetic , thank you Krishna and Vasudeva), Bhakti, Jnana, and Karma.
2) Praying to Rama is silly in my mind, because ultimately, what is Rama? He is God incarnate and it is God and not Rama that you give your prayers to. Rama is neither the origin of Krishna and nor is Krishna the descendant of Rama. They are the same in spirit, and ultimately, that is all that counts.
3) To ask such a question on this forum is pure fallacy. On a Hindu forum, most people will suggest you read the Hindu scriptures first before anything else. Swami Vivekananda would probably suggest you read the Bible and Koran too, but after fully understanding the Hindu philosophy.
Swami Vivekananda was a very liberal and free thinking Hindu, in my opinion. Look up and read his works and you might find what you're looking for.