No
No hyphen is needed for world class. World is just an adjective that describes class much like (for example) upper class, which also does not need a hyphen.
There are specialized directories listing Yoga Studios around the world. You will need to look for an instructor that meets your needs. For example, instructor's experience, location of the class, class timings, reviews on the studio etc. One of the Yoga directories is listed below.
It does not need to have a hyphen! :)
No, the word "nineteen" does not need a hyphen when written numerically.
pilates and yoga help!! x
Yes, one is said to be enrolled in a yoga class.
Yes, in this case "seventh-grade class" should have a hyphen to show that the words "seventh" and "grade" are functioning as a single adjective modifying the noun "class."
No
You don't necessarily need yoga pants, but it would probably help. You can purchase a very cheap pair at Old Navy, if you don't live near one you can check www.oldnavy.com.
I do not believe that multitasking is supposed to have a hyphen.
It's not a word in the dictionary, so yes, use the hyphen.
You typically need only capitalize after sentence-ending punctuation, which a hyphen is not.