Every year or so you should change it if you keep waxed and shoot it a lot.

Wax your string often with string wax. This will keep it lubed and prevent wear.

Sometimes like you found out, they will go without warning. A lot of times its under the end servings near the cams where it makes sharp turns.

There are better strings than come on a stock bow. Companies such as winners choice or vapor trail, as well as members of this board build quality strings that offer more performance over your stock string.

It should say the length of your string and cable on a sticker on your limb. If not, a proshop should be able to find out.

You should probably go ahead and replace the cables too so that they get broke in together.

I would take it into a shop and have them install the string and check over anything else that may have gone wrong when the string broke.

Cost depends on who builds your strings and if you have them installed or not.

Yes they will put your peep back in for you and you will have to breakin and resight your bow when you get new strings.

Hope this answered many of your questions.