No. 1 and to You are a young'n so we'll let you off this time, but swearing here is not considered "with it" nor "cool" even if you are over excited.

No. 2 Any after market exhaust without baffles is going to be loud. Also MTC exhausts have BS stamp that is valid only when the baffles are in place, without them, you are riding illegally. If you are buying that bike, better get in touch with MTC at this email address so you can order a set of baffles which are cheap too.
sales@mtcexhausts.co.uk write the email in attention to Martin

No. 3 please find this link which explains all the variant of stage 1, 2 and 3 but bear in mind all figures and HP results are related only to DNA filters and not K&N they are different companies and have different performance click here: http://www.captnmoto.co.uk/Stats/XT660ZStage123.pdf

No. 4 Enjoy the forum, the people here will go out of their way to help you feel as part of a big family, myself included even if I had to tell you about No.1