First off, welcome and congratulations! (For the sprog, of course.) What a lot of questions you have - good practice because in an eyeblink your new son or daughter will be asking you "Why?" every second word...
I was going to recommend the
NekoWiki Disk Cloning Guide
, but it sounds as if you got past labeling and partitioning. Some old SystemV-ish systems had some lame issues around their implementation of pipes, but I'm thinking of old SCO UNIX rather than IRIX - I've done what you're attempting to do with no problem.
Filesystem layouts beyond / and /usr were fairly variable amongst UNIX vendors. /home was in use a lot of different places - numerous university Sun-3/Sun-4 installations come to mind - but AFAIK was not an out-of-the-box convention until Linux distros made it so. So you'll see /opt on some systems, /var on most everything unless you go waaaay back, etc.
For TOD battery issues, note that per
this post
the battery location will require minor disassembly of the machine. There's also
this guide
by our own
pentium
for hacking in a coin cell battery holder. He references some additional sites, and searching for "NVRAM battery replacement" is usually fruitful.
That's it for me, for this sitting. Enjoy!