When I hear numbers like this, my gut tells me that there must be life out there somewhere.
The number of galaxies is mind boggingly large (around 100 billion in the observable universe), and the number of planets even larger, but there is no reason that the probability of life couldn't be even more mind boggingly small.
It seems plausible that getting the sustained chain reaction of life going in a soup of organic molecules and not immediately interrupting it may be at least as unlikely as randomly guessing a 256 bit password, in which case it will certainly never have happened a second time in the volume of space time we call the “observable universe”.
Life on Earth took 10 billion years from the Big Bang to emerge. No evidence indicates any other planet did it before us.
I think most galaxies we see are younger than that.
It all breaks down at some point for it to be interstellar or maybe even properly interplanetary.
Unless you mean something very different by "properly", it's pretty clear that there will be multiplanetary life out there if it exists at all.
The engineering and resources really start to look lot harder if you push it to meaningful population numbers. Let's say couple hundred or thousand on regular basis.