Taking off one inner and outer link should be close enough. If this was a 1x system you might need to be more concerned but it shouldn’t be a problem with 2x.
The oval chainring has the same perimeter/teeth as a circular chainring so there’s nothing weird with that for chain length. When the oval is widest it’s narrower at other parts and vice versa.
I usually size my chains for 2X by going into the small-small gear combination and having the chain be just long enough to avoid having the bottom part of the chain rub on the rd cage or the portion of the chain that rolls off the upper pulley. So I’m basically looking for something like this when in the small-small combo: