Depending on the types of music you listen to, especially opera and classical, yes, iTunes finally supporting gapless playback was a pretty big deal. Prior to iTunes 7, there were a couple of tedious work-arounds to minimize the iTunes-enforced gaps between tracks, but they're no longer necessary. You'll appreciate it also if you listen to live concerts, or something like 'Dark Side of the Moon,' where music was meant to be heard flowing from one song right into another.
You mentioned that you controlled your Mac Mini via a powerbook. This sounds ideal but how does this work? Does this require special remote control s/w or is this functionality built into Mac OS X?
It works by taking advantage of a cross-platform technology called VNC (Virtual Network Computing) a free client called "Chicken of the VNC" (there are other good ones) and yes, Apple builds remote desktop functionality into every Mac, you just have to allow it in System Preferences > Sharing > Apple Remote Desktop > Access Privileges > VNC viewers may control screen with password.http://www.macminicolo.net/Mac_VNC_tutor.html
There are also a bunch of dedicated apps and applescripted stuff which can control iTunes remotely, look into NetTunes, RemoteTunes, if you don't want to VNC into it from another Mac. This has been mentioned on other threads, so poke around, you can also run VNC on a Palm, there's Salling Clicker as well for BT or Wi-Fi phones and pdas.
Some complain about lag, but with most of our Macs on gigabit (including the Macbook which is the one actually connected to the HDTV, AVR and a bevy of firewire and usb externals) with a relatively interference-free wireless g setup, VNC zips along nicely for us. I prefer VNC (over a remote control iTunes only app) not only because I don't have to turn on the HDTV if I don't want to, but also because while I have the Macbook desktop open on any other Mac in the house--usually a 12" Powerbook--I can do other things besides accessing iTunes: check my EyeTV recordings and schedule, export some shows to iPod format for my wife, rip a dvd, move files around and clear up some hard drive space, whatever, all remotely. VNC also allows me to select and de-select Airtunes streams to other locations, say to an Airport Express in the bedroom. (Which would all be in sync, locally and remote.)
So, at the moment, it is ideal, as long as you don't prioritize a svelte touchpad handheld controller like Jonesky, there's nothing yet so elegant, at least until that new touchpad iPod with built-in Wi-Fi and BT is released. I couldn't care less about the iPhone, I want the iPod sans phone as the ultimate Mac HT controller.
Ripping, storage and backup strategies are probably too vast to re-visit on this thread, externals and NAS have been covered on other specific threads. (I do Apple lossless, and have my iTunes library in a dual drive external enclosure, so I always have an automatically mirrored backup "copy" on a second hot swappable drive tray.)
I haven't thought much about storage yet but you are right about backup.
Just remember that "storage" is not necessarily backup, and that "redundancy" against a particular drive failing (a la RAID 5) is not necessarily backup, either. The situation is a lot more nuanced, depending on how you value your time and data.