A bushing involves filling the peg hole with a tapered dowel and re-cutting a new smaller hole for the peg to avoid excess pressure on a crack when turning. This is a big question and everyone has a different answer. It really depends on the string and how often you play. Some sooner - some later. If the answer is 'yes', then replace them.
Strings come in a great variety.
Perlon core, steel, rope core, pure gut and wrapped gut. Many fiddlers like the steel string for its power. They are made by most companies. Experimentation and experience will help you choose your string. Remember to wipe the rosin from the strings frequently and to change strings one at a time.