If EveryMac says 16 GB, then you can trust it.
I assume an EFI upgrade is relatively painless (like a BIOS upgrade on a PC), but make sure all your ducks are in a row before doing it. I think I did it on J's Black MacBook, but it didn't enable any magic - it was just to try to keep it as current as possible.
That Apple link was just for Lion. They eventually stop updating pages for the older OS versions. There's a similar page for Yosemite (which I can't find at the moment). Note that it apparently works with 2009 and newer iMacs (I don't recall if yours is older or not) - http://www.tekrevue.com/tip/ins-outs-imacs-target-display-mode/
The Mac Mini used to be the most reasonably priced expandable Macs. The latest versions are more locked-down than the older machines - https://www.ifixit.com/Teardown/Mac+Mini+Late+2014+Teardown/30410
This one is similar to that white MacBook in many respects. It's $399. My MacMini Server is still working fine (running 10.9.5 without the Server addons). It has 8 GB (I see that it can go to 16GB with a firmware upgrade. Thanks for finding that!).
Dunno if I'd get a 2014 MacMini, as it has soldered RAM, but the older machines are well worth considering if you're worried about needing/wanting more than 8 GB of RAM.
Have fun!
Cheers,
Scott.
That Apple link was just for Lion. They eventually stop updating pages for the older OS versions. There's a similar page for Yosemite (which I can't find at the moment). Note that it apparently works with 2009 and newer iMacs (I don't recall if yours is older or not) - http://www.tekrevue.com/tip/ins-outs-imacs-target-display-mode/
The Mac Mini used to be the most reasonably priced expandable Macs. The latest versions are more locked-down than the older machines - https://www.ifixit.com/Teardown/Mac+Mini+Late+2014+Teardown/30410
This one is similar to that white MacBook in many respects. It's $399. My MacMini Server is still working fine (running 10.9.5 without the Server addons). It has 8 GB (I see that it can go to 16GB with a firmware upgrade. Thanks for finding that!).
Dunno if I'd get a 2014 MacMini, as it has soldered RAM, but the older machines are well worth considering if you're worried about needing/wanting more than 8 GB of RAM.
Have fun!
Cheers,
Scott.