but it’s cool to imagine a universe where life was incredibly abundant

There was probably nothing but helium, hydrogen and a tiny bit of lithium at that period.

Interesting theory, I'd never heard of it before. All of the sudden, "a long time ago, in a galaxy far, far away", actually seems plausible (although this theory looks like it came well after SW in 2014).

The actual paper about it: https://lweb.cfa.harvard.edu/~loeb/habitable.pdf

More weird to me is that, at some point before the first stars, the entire universe glowed through the entire rainbow, so there is a moment when, were you to travel back in time, the entire universe would glow blindingly green.

I'm skeptical of this. Life doesn't just need a certain temperature, it needs to convert lower entropy energy to higher entropy. A uniform environment temperature does not provide any usable energy. You would still need a star or some other energy source.

Well, "life as we know it". But for all we know energy rather than matter-based beings could have existed more readily back then, and perhaps struggle to exist now under lower density conditions. Thereby making that earlier era more habitable for their type of life, even as our current era is more habitable for our own type.