Luciferianism is a doctrine based around the seeking of knowledge, the respect of us and others, and betterment of us and humanity in general. We are generally agnostics, and we can't judge the practice of other Luciferians, as long as they respect the general values of the philosophy.
Is the character of Lucifer seen as an actual entity or more as a symbol of an idea in Luciferianism?
Depend on the Luciferian. There is some that are theists, either about the pagan Lucifer, or the Greek Phosphorus, or the Bible Lucifer. I consider the latter's to be closer of Theistic Satanists than Luciferians. But the general principles are to inspire ourselves from the positive traits of Lucifer, literally translated as "light-bringer", and the associated Venusian divinities. We have theists, but they are not obligated to a practice. They can worship whatever god they want. The principles of Luciferianism as mainly centered around shared values and a thirst for knowledge and its application for oneself and others.
Are Lucifer and God enemies? allies?
It definitely depends on the beliefs. Satan, Lucifer and the Devil we're associated with each other pretty late in the Bible history. Originally, there is no mention in the Tanakh that the snake is the devil, Lucifer or Satan. It is specified that God created all creatures in the Eden good, including the snake. In that optic, the snake did as intend by God's plans. Later in the Tanakh, in the book of Job, Satan is also clearly working for God. So, if we follow that path, everything is planned in accordance with God's plan, including Satan rebellion, they are allies. But in Christianity it is clear that they are enemies, and the devil was later associated with Lucifer. But in any case, that would imply that we Luciferians are theist or that we believe in Christianity.
Luciferians are the very epitome of social realists in that, we don't see things through blinders, we see them for what they are. Our happiness is in our hands...period! No gods or devils ruling over us, we are our very own creators and ultimately destroyers. We are the Alpha and the Omega of all things in our reality, a reality forged in our own perceptions of the world around us. Each and all person's perceptions differ from the next person's and therefore religion and dogmatic stigma are dissolved by those who understand this, as there can't be strict dogma without herd mentality.
Just as Lillith is Lucifer's counterpart, all things have a duality, including human beings. We are happy/sad, intellectual/primitive, aggressive/passive, sexual/abstinent, masculine/feminine, active/inactive etc... Each and every human being is a walking parody of themselves who through life experiences have had their perceptions of the world shaped and came to understand them with time. Understanding and application of what is understood are core components of any true initiation and/or progression in Luciferianism.
Ain Soph Aur