yes
No, it's a metaphor, with a more exotic sense than a simile. "She wanted to be like a blade of grass amid the fields" is a simile.
false
eagles are bigger than humming birds
his bathtub contains more water than a water tower
More than 50,000
more than just friends by mariah carey
An ordinary simile is a comparison using "like" or "as" that is relatively straightforward and brief, while an epic simile is a more elaborate comparison found in epic poetry that can extend over several lines or even multiple paragraphs. Epic similes typically use more exaggerated imagery and involve more elaborate descriptions than ordinary similes.
No, "than a" by itself cannot be a simile. A simile is a figure of speech that compares two different things using the words "like" or "as." For "than a" to be part of a simile, it would need to be included in a larger phrase that establishes a comparison, such as "as brave as a lion" or "faster than a cheetah."
metaphor
No, there are far more than four bald eagles in the world.
rapid water
"More fierce and more inexorable far than empty tigers or the roaring sea."