Will publishing all my papers in a single journal endanger my career?
Your first few papers don't determine your career. The answer to the title question is, of course, &quot;it depends&quot;. If your research focus is narrow, especially narrow, then there are fewer journals that are appropriate venues and the others won't have appropriate reviewers in their &quot;stable&quot;. But continuing to publish in a very low impact journal would have negative consequences, that aren't the case here.
I'll guess that &quot;a paper in the same journal&quot; is a better outcome than &quot;no paper&quot; at this particular point in your journey, so your advisor is likely giving good advice. I doubt that an editor, even one who knows you will bias decisions in your favor if they want to keep up the reputation of the journal.
But, the indicators seem to be positive, not negative; getting published in a good journal.
You can also ask the editor of the journal you submitted to about the likelihood of a decision in a reasonable time frame, saying that if that isn't possible you will &quot;be forced by circumstances&quot; to withdraw the paper.
I'll also note that, assuming everything you say is accurate, that people believe in you and your work. That support alone should lessen your fears about getting a good position in the future.