Congrats on the new iMac! Mine is out for delivery today too, very exciting day. From what I've read from other memory upgrade threads it seems prudent to ensure everything is 100% with the stock iMac (included ram) before then shutting down to upgrade it. Maybe you did do all this before removing the plastic .
In my case I have four sticks coming (also today) but I am likely going to be a little neurotic about it and add each matched pair one at a time in the recommended xoxo pair configuration. (I'll look it up when the time comes.)
The sticks are all Crucial and the same size and order, so there is very small chance of match issues, but something looks off at some point then doing it step-by-step it will have seemed wise. If not, I'll probably feel I wasted 10 minutes.
Are you coming from a MacBook and are accustomed to a trackpad? If so, I'd recommend the external Magic Trackpad if you can budget it – especially if you find you don't warm up to the mouse. I actually picked the trackpad in my BTO configuration as I didn't want the mouse – I have an old dusty Magic Mouse anyway. I've been using an external trackpad for years and (personally) prefer it. Bonus: unlike the mouse, you can still use the trackpad while it is charging.
(Yes, now I will have two trackpads but my iMac vs work MacBook need to serve different purposes and will both be regularly setup. I sometimes also use the trackpad from my iPad. Better two as I can keep them paired to different devices, rather than a mouse I'd never use.)
Anyway, enjoy your new Mac!
Thanks! No, I upgraded the ram before turning it on. The issue was how I was trying to turn it on (holding power button forever, then again, which was just resetting it. I'm used to noise coming from things when I turn on the power. This baby is SILENT. Everything works great. I was up until 3am last night playing with it, and back at it today. Have an external SSD partitioned and Time Machine already working. Did an iPhone backup to test out before Friday. Synced everything I have (which is embarrassingly a LOT! hahaha). Oh, had to update OS right out of the box. Went smoothly. Seriously, this thing is amazing!
I'm getting more used to the mouse. I think if I had to complain about something, it would be the infamous charging port at the bottom. That must be the biggest bone-headed move by Apple in recent years. But, oh well.
Good luck with yours, and I hope you enjoy it as much as I enjoy mine!