Re:
Respect! That's an awesome job done there. Did you find the job more straightforward than feared? It's always worth doing a fresh clean install (after a backup) as this can wipe a lot bugs and problems. Did you need to update the firmware after putting the new RAM in?
In case the iMac ever dies, it's worth cloning it in its entirety asap to a formatted external hard drive. Had some problems with mine a while back when it kept switching itself off and restarting itself. I bought a slim pocket-sized Seagate 1Tb usb drive (£40-£50), reformatted it to Mac OS Journaled extended, then left the iMac cloning/copying itself overnight to the Seagate. Once this is done, you have your entire iMac (everything – OS, apps, all your files, data and settings) on a tiny portable drive safe. You can choose to startup from this clone and run it like the iMac.