Many professionals will own one good instrument. Sometimes, if they own two, one will be used for certain pieces. Each instrument sounds different, so depending on the sound they want to deliver for...
The fiddle has "strangs" (say it with a southern drawl, and the violin has "strings". there is no difference.*fiddle there is no real difference, but the style of playing is different.
If you go to your local music store where you can rent instruments, they can usually measure you for an instrument. There is no definite "size" for skill levels. A professional player can have a...