You might want to contact a publisher first. They will take care of most everything. And if they would accept it, then you may get published. But it doesn't mean it will be bought up because who would buy classical music from someone named Spatula? It sounds more like a punk band in the UK.

Or the other route if no publisher will buy your composition is to publish it yourself. If sucessful, then you reap 100% of the profits. This is how many small publishers and record labels start: because big houses think their works are not worth their brand name.
And I would really doubt that 5,000,000,000 copies would sell. There are only so many people on this earth (6,000,000,000).