Avenida/Calle

Avenida/Calle
 

In Spanish why do the numbers for Avenidas come before the word avenida, but the numbers for Calles come AFTER the word calle??? La Quinta Avenida VS Calle 5

That's too narrow a correlation.

There are certainly Avenues that are followed by a digit, like Avenida 1, Avenida 2, etc. And there are streets similarly designated, e.g., Calle 1, Calle 2, etc.

Fifth Avenue is La Quinta Avenida because an ordinal number is being used, and distinguished. You can find First Street, Second Street, etc. in cities, as well. Sometimes they appear in the same form as Fifth Avenue (distinguished with the article la), but it's more common to see Avenida Segunda, Avenida Tercera, etc., with the trailing ordinal.
In Spanish, the ordinals are sometimes represented with an abbreviation, consisting of a digit and a letter (sometimes two letters), like the English 1st, 2nd, etc.

So, fifth avenue could be written La Quinta Avenida, Quinta Avenida, Avenida quinta, Avenida 5, Avenida 5a (and that 'a' will often appear in superscript).
The same numbering patterns can be used for streets.

I agree with Rusty.

Just for the sake of fun-facts:
In Mexico City, you may find a street named "Poniente 8", but in Puebla you will find an "8 Poniente". :)