We can certainly see they are the same Location (Prometheus and Alien Covenant Mountains)
Its thus interesting if Planet 4 Sacrificial Scene leads to those Engineers, and they are connected to us in some way.
I feel its a way for them to SHOW us the Audience there is a connection..... But its in a Easter Egg way.
I cant see how it was taken in any context to show that Weyland had Knowledge of Planet 4 at the time of Davids Creation and so over 60 years prior to Prometheus.
Maybe its just one of those things that is for us a Easter Egg, that confirms to us the connection, but its not in no way meant to show that Weyland had prior knowledge or been to Planet 4 (via a Probe of anything).
Thats just my interpretation though.
Regarding leaving Planet 4, i think it depends if we can take the other Ships in the Hanger as Canon, as this Scene was removed and it fits better if we accept there was no other ships on Planet 4.
I think David will be off to Origae-6, i think it makes sense for David to go down first and get some Black Goo and few Eggs from Planet 4 prior to his journey to Origae-6
I will safely assume years latter a Engineer Ship or Ships arrive at Planet 4 and then they will want to catch up and have a few WORDS with David and so they will many years latter be off to Origae-6 too