Head Unit question

[nseller324]

I recently bought a 2009 Yaris sedan, and well the sound system sucks! I have read several posts on how to install the head unit. I know I need the toyota part and the metra wiring harnes and install kit. I am planning on doing this myself and have some questions that i cant seem to find the answer to.

1. does installing it this way require any sodering or changing of the wires etc. I need to be able to return it to stock stereo if need be.

2. does this mess with any of the computer things at all? will I lose any features? ( I am new to all this and have no clue!)

3. I already have an existing deck from my old car I want to be able to use this one again, will it fit if I use the setup described here http://www.yarisworld.com/forums/showthread.php?t=28064
( I posted a question there and didnt get an answer... )

deck I have is this one
http://www.onlinecarstereo.com/CarAu..._KDC-X792.aspx
It's an older deck, a few years, but it works great!

4. if I am to hook this up do I need to do any rewiring for the speaker or will I
be able to plug and play the existing speakers into this, I will be replacing them with the infinity speakers I have soon but at the moment I want to get atleast the deck replaced. Also have an amp and sub I will be getting installed also ;)

sorry for the lengthy post, and I apologize if these seem like stupid questions, I just want to make sure I do it right!