Sleek, I am a licensed journeyman plumber in Texas. As has already been said plumbing codes differ from state to state and even from city to city within the same state. What you are describing sounds to be a very involved plumbing job and although it could be expensive I would recommend having a licensed plumber do the job. In Texas as a homeowner, you are allowed to do your own repairs, but may still be subject to an inspection being that you are in the city.
Also keep this in mind; the previous plumbing may have been installed incorrectly and more than likely will not be up to current code depending on the age of your home. And if you ever decide to sell your home and the plumbing isn't properly installed, when a home inspector sees this it will de-value your home. Just some things to keep in mind if you try to "copy" existing piping.
Now if after reading all that, you are still wanting to tackle a complete re-pipe job, keep this in mind. There are two different types of pvc fittings. The one you want to use on sanitary wast and vent piping will be marked with the letters DWV on the fitting. These fittings have a "hub" with a raised area that is bigger than the rest of the fitting. The other type will be pressure fittings and will be the same outside diameter as the rest of the fitting. Do not use these for wastes and vents.
Pex is a great material but for the average homeowner, I would suggest plain old pvc for your water piping. The pex will require an additional investment in regards to the tools needed to make connections. I'm not a fan of the crimp connections anyway. The other kind of pex uses a tool that costs about 3 to 4 hundred dollars.
Make sure your waste lines have good fall, slope, on them! When you put the level on them, torpedo level is fine, make sure the bubble just barely breaks the line. There are graduated levels out there that show slope in 1/8th inch increments. And use schedule 40 for all your piping!! The thin stuff just causes more problems later on down the road.
Hope this helps. Good luck to you.
