If I get +2 A-Arms for my LTZ400, do I need to replace the Shocks, Break line, Tie Rods, or any thing. Can I leave the stock stuff on?

I think it depends on what a-arms you buy. Some are designed for longer shocks, some are for stock shock length. Some come with extended tie rods, some don't. But if you are going to be doing and jumping you will probably want to look into aftermarket shocks, due to the added leverage you are adding to the stock geometry.
www.z400central.com can get ya hooked up im sure on parts. If the link does not work try http://suzuki.theatvchannel.com/

If you buy +2 arms you gotta get longer tie rods but they usaully come together. The brake lines dnt really need to be changed unless u go long travel