Hi
A couple of basic gotcha's with hard plumbing:
1) Tough to take apart to haul everything away for cleaning.
2) No easy way to see what's going on in the lines without site glasses.
3) Rigid / heavy pipe can be a pain. Even tubing is a bit of a hassle.
4) There are a *lot* of ways to hook things up and run stuff. Just when you think you have the ultimate setup along comes an idea and you change it all around.
Unless you have a very good idea of what you are doing (as in you've been doing this for many years) I'd say number 4 is the biggie.
Bob