The plumbing codes list galvanized iron pipe, copper pipe, CPVC and in most localities PEX or PEX-AL-PEX as approved for potable water distribution lines within a house.
While we could make a long list of pro's and con's for each type of material allow me to cut to the chase. While I do personally prefer copper, nevertheless, in my humble opinion copper or PEX should be thought of as about equal in overall quality.
Although very seldom used today, with an expected service life of 60 to 100 years, galvanized iron pipe is still a very good material although it is very expensive and labor intensive to install. As a general rule galvanized iron pipe is considered cost prohibitive for residential construction today.
As a rule, CPVC is generally thought of as the bargain basement material for potable water systems, although in regions where they have acidic water that would cause pin-holes in copper, CPVC is then the material of choice.
Some will argue that PEX is the material of choice for regions with acidic water, but it must be remembered that the fixture end stub outs used in a PEX system are principally made of copper and as such they would be subject to the same corrosive effects of acidic water as would copper pipe.
Taking this discussion to the next level. If there is any condition in your water quality that would adversely effect the pipe material I have to ask myself, what does that condition do to your body over a prolonged period? Here again, in my personal opinion, when you have water quality issues that are detrimental to any pipe material would you not be better served by installing a water treatment system to correct the problem rather than look for a more tolerant pipe?
Now in regards to sanitizing the potable water distribution system. The major health concern is the formation of bio-film. It must be understood that bio-film grows very slowly and is easily controlled by chlorination, therefore if you have a chlorinated municipal water source your risk of bio-film is greatly diminished, especially in the areas of frequent water use such as your kitchen or primary bathrooms, however, in nearly every structure today we have pipes and fixtures that are seldom used, such as a guest bathroom, perhaps a faucet or bar sink in the basement or the outside hose bibs during winter months. As the water remains basically stagnant in that section of the piping the chlorine in that water will dissipate leaving the standing water in basically a stagnant condition. If you have a chlorinated municipal water supply the immediate solution is to just open the faucet and let it run for 5 or 6 minutes to flush the pipe.
If you water supply is not chlorinated we then turn off you main water shutoff valve, completely drain your water system, then refill it by pumping in a sanitizer solution. The solution is allowed to stand for about 1 hour, then the system is again drained and the main water supply valve is opened again.
That may seem like an expensive method but in reality it is quite inexpensive. The sanitizing agent is simply a solution of water and common chlorine laundry bleach and the amount required is not nearly as much as one might think. To give you an idea of how much solution might be required consider the volume of your pipes"
1/2" pipe.....1gallon per 98 linear feet
3/4" pipe.....1 gallon per 44 linear feet
1" pipe........1 gallon per 25'
As you can see from those volumes, in most instances it will require 10gal or less to completely sanitize the house piping system.
Now in regards to your question about the PEX gage.
Principally there are three diameters of pipe commonly used in a PEX system.
When PEX first came on the market it required a separate crimping tool for each size of pipe and the tools were selling for about $125 each, plus an additional $8 to $10 for the go/no-go gage.
They are now making some crimpers that have interchangeable jaws thus you can get a single crimper handle with a full set of jaws for about $150.
On the other hand, as PEX becomes more and more popular in a region the local tool rental companies are often now stocking the tools for a moderate daily rental fee.
And last but not least, your concerns about soldering copper.
Fortunately for me, I was in the refrigeration & AC trade for a number of years before I went into plumbing. In refrigeration work all our copper pipes had to be brazed to a gas and vacuum tight standard, which required the use of acetylene torches. After that experience I found soldering copper to be almost second nature.
i could not begin to tell you how many people I have taught to solder copper over the years, yet in each experience one thing proved to be true. In the beginning the idea of soldering copper seems a bit intimidating, but as is true of all things, with attention to detail and a bit of practice it becomes fun and easy. If I could make you no other suggestion, i would suggest that before you begin a house project get a short length of scrap copper, the greener or blacker the better, and a dozen or so fittings, then just play with that until you get the feel for the process. My 11 year old niece took the practice idea to the next level. Instead of just soldering fittings on a section of scrap she made a little high chair for her favorite doll by soldering copper pipe.
Here is a website were you can download the complete "Copper Pipe Handbook" in PDF format
http://www.copper.org/resources/pub_...e_handbook.pdf