You're gonna need a bigger coffee pot.
I'll start with question 2 as I think it feeds question 1. The assumption you make in your answer is that there are many alien civilizations. While I find the scalar and wormhole stuff interesting, let's focus on the conventional. Our travel to Mars, our neighbor, has been what so far? Robotic. Why? Because of the immense process of sending a human. Maybe someday we'll go. It would be awesome, but robots will always be easier.
Fast forward to travel through the galaxy and the advantages of sending robots are exponentially increased. Can you imagine a circumstance where any "conventionally" traveling species would send living beings first? If there are multitudes of species as you posit, I find it wildly implausible that the vast vast majority would do anything other than send robots first. Very soon, at the current rate of technological advancement, we will be able to build robots capable of self replication. It has been estimated that such devices could physically visit and colonize the ENTIRE galaxy in 250,000 years. They are commonly referred to as Von Neumann probes. 250,000 years is not a blip when compared to the age of the galaxy. Where are the probes? They simply would have to be here already, multiple times over if your assumptions are true. But they aren't.
As for question 1, the scavenger threat could be a real one not just from the aliens themselves, but from the self replicating probes who need materials. If they're shooting off in all directions from each solar system, they'd need a lot of replicant building blocks. In our limited exploration of Mars and the Moon, has there been any evidence of this? What if the probes needed all of Jupiter but could leave everything else alone. That would throw the balance of the system way off.
If we ever venture to the stars without finding a shortcut it will almost certainly be in this manner, at least to begin. It is plausible that DNA maps could be embedded into these probes and programmed to be adjusted to meet the characteristics of new homes.
And yet, no probes from anywhere ever. No signals from anywhere ever. I wonder why. Maybe we should ask Sheldon.