difference violin vs fiddle mandoline versus mandola....

ummmmmm.......

here is the definition of a mandola according to Mandolin Cafe.

Mandola:

In the US, this term is usually applied to an instrument tuned one fifth below the mandolin, analogous to the viola: c, g, d, a. Europeans would refer to an instrument of this size as mandoliola, mandola in C, or tenor mandola (although this latter is a bit of a misnomer given the instrument's alto range). Some instruments have been made with an added fifth course at high e" to provide a kind of mandolin/mandola hybrid.
so a mandola is to mandolin as viola is to violin.

now the next question. they are two completely different things.

now the last question is one that you could get lots of answers on and whoever answers it swears theirs is the truth.
my answer:
"If you want to play fiddle you play fiddle. If you want to play violin you play violin"
in other words they are the same thing but played different...but sometimes not even that.
they are tuned the same and all, the "hardware" is the same too. its not in the instrument but the player.

if you really want me to i can answer the banjo question in more detail. but i thought that answer was simple enough.
hope this helped

no questions about the Dulcimer?

A.

I would respectfully disagree! A fiddle is carried in a feed sack or burlap bag...a violin is carried in a case...

Perhaps I can help with number 4:

La Guitarra Mexicana (Mexican Guitar),  Think Classical... nylon strung in various body volumes and scale lengths. Played with the fingers only as in classical.  I'm thinking that the style of play rather than the instrument itself is the major difference.