zfs drive configurations?

I would appreciate some help understanding what drive configurations
work best with zfs, if someone's got a spare moment to help me out.

I've got a machine I'm putting together with 5 drive bays, and I'm
trying to work out what combination of drives to use.  The appeal of zfs
is that I can start with relatively small drives, and replace them, on a
one-by-one basis, as they either die, or I get my hands on larger ones.
Is this possible?

What if I have 5 200gb drives configured as a raidz pool, and then I
replace one of the 200gb drives with a 400gb one.  Operationally what
would I do?

Joe