Never, ever even consider galvy pipe for new construction! There are so many causes of galvanic corrosion and all of them attack galvanized pipe. As soon as the zinc coating is gone, the rest of the pipe starts going.
Copper is great--it's expensive and takes time and expertise to run--but if you have any galvy anywhere in the system it will destroy the galvy even faster. Dielectric unions are a myth (as is using brass fittings) as all plumbing is eventually connected through grounds.
PEX is great, but, as mentioned above, keep it out of even indirect sunlight. I certainly don't mean you have to run PEX at night and have it buried before dawn. I run exposed PEX in the brewery, but am careful to keep it where direct or nearly direct sunlight from windows doesn't hit it. Yet to have any fail. PEX is highly resistant to freeze damage (if you get the right kind), but keep in mind that the metal fittings are not!
A hose bib takes a beating. If used as a hose bib and not just a drain, it needs to be mounted securely--not just hung from PEX. If you're installing a whole-house drain--a very wise choice--be sure to slope all lines to drain back to it. We used an exterior hose bib on all our new or remodel work as it drains the water to the outside. But I live where sub-zero winters are the norm, not the exception. It's common practice here to shut off and drain the house if taking a winter vacation--even just a few weeks. Just one of the ways you can tell the old hands from the newcomers.
