The way he said it sounded as: [I'd say it even in english -you're doing very well-, but let me speak] It's like a conversation technique he had worked out to stumble the other person to stop talking and become more agreeing; diverting his attention by English, and conveying the meaning which was agreed to.

احنا موجودين، وكلنا نتكلم لغة واحدة، اشرب من اي نهر يرويك.

أو = Or أم = Either

In addition to the above, Linguist.io I like this website because it teaches in a 'smart' way, it starts with the more commonly used words.

... وهكذا*

It depends on the dialect, which is also noticeable within one country.

Vowels are not written as letters in Arabic. It's possible to know which vowel to pronounce if you had the حركات (form character) which denotes the way the letter must be pronounced. In Arabic, basically, there are 3 ways you can pronounce each of the 28 letters. e.g., the letter أ , is pronounced as A. أَ = Aa إِ = E أُ = Ao If the word had these forming characters (which signify the vowels), it is possible to know how the word is pronounced. Arabs, however, figure it out intuitively.

They are being used interchangeably. Exact meaning of شغلات is occupancies. and of اشياء is things. شغلات usually is referring to something that is time-occupying (consuming). For precise language, شغلات is better to be used with actual time-consuming activities.