Yes, I think that God should be called father. One reason is that he is Jesus Christ's father. In Matthew 3:17 it says the following:
And a voice from heaven said, "This is my Son, whom I love; with him I am well pleased."
The voice is God. He calls Jesus his son, which makes God his father.
A second reason is that God created all of the Earth, the universe, etc. He is the father/creator of everything. It's common to call the creator of something "father." Mendel is the father of modern day genetics. Geppetto is the creator and father of Pinocchio. Darwin has been called the father of evolution (although it's more accurate to say that he is the father of evolution by natural selection). All of these men have the title of father applied to them, because they created something. God created everything, so he can rightly be called father.
In Romans 8:15, Paul writes that believers are to pray and think of God as "Abba, Father."
Matthew chapter 6 verses 6-9 says the following:
6 But when you pray, go into your room, close the door and pray to your Father, who is unseen. Then your Father, who sees what is done in secret, will reward you. 7 And when you pray, do not keep on babbling like pagans, for they think they will be heard because of their many words. 8 Do not be like them, for your Father knows what you need before you ask him.
9 This, then, is how you should pray:
“Our Father in heaven,
hallowed be your name, . . . "
I would say that with the support of scripture and with the human interpretation of how God functions in people's lives, that yes, people can address God as father.
The above answer is highly sufficient. I just added a couple quick notes for your question.
The top of the cross is what we symbolize during the "sign of the cross" Father-Son-Holy Spirit. Depending on your religion, I would say yes, God=Father.
However, it can feel confusing in Catholicism. Priests are often referred to as father.