does that suggest that the filter for life given Earthlike planet is pretty easy to pass?

Robin argued that it doesn't in his Great Filter article. If creating us takes several hard steps, hard enough that the expected time is much more than the time up to now, then for us to exist now we'd expect the first step to have happened quickly. (The detailed math is at a broken link.)

best estimate for when some interesting replicator populated a significant part of Earth?

There's evidence for very early life (e.g.) but I gather it's not nailed down.

Do we have evidence of any pre-RNA replicator of significance?

Here's a pop science article on a plausible precursor (which I can't competently evaluate).