I love that you are choosing this topic to talk about!
One of my favorite books I read in high school talked about the evolution of the English language over the centuries and how it drew from all the elements that you are talking about.
At the end it concluded that there is no "pure" form of English, and that the language at its essence is changing and constantly mutating, and that is a good thing =)
I find the history of the English language fascinating. It's always funny when you hear a foreign speaker use an English word, except it's not, it's from their own language and was incorporated into English hundreds of years ago. I've heard it called a living language and it seems an appropriate description.
Sometimes English can seem so complex, but in other ways it's so simple. When a foreigner is not fluent with the language they can often still make themselves understood, because English is so flexible. Word order can often be swapped around and still make sense. I can see, in many ways, why it became the go to language for communicating internationally and I don't think it's purely because of the British Empire. Every country that speaks it as their main language uses some different words as each has evolved separate to British English.
And there are so many foreign phrases that we use regularly (and I guess this is subject to be different depending on where you live what your circles are etc) but there are many french/spanish/yiddish phrases that are common knowledge and people find themselves using them even if they have zero knowledge of the actual language that these phrases are borrowed from.