The difference is that the CWT418MFG-1 has PEX supply lines, meaning that if you have PEX supply in your home currently this one would be a little quicker to install. The CWT418MFG-2 has copper supply lines and would work with most homes existing supply lines. If you are having a licensed plumber install this unit he will be able to make either of these units work for you. If you have copper supply lines in your home currently you may need additional parts for the connection if you go with the CWT418MFG-1 (PEX Unit)
Yes it does come with the push plate.
You would need to order the 2x4 outlet kit for this installation. It is part # THU343. The tank is the same for either installation.