a. Was the original Amiga level editor ported to other platforms, or were were the official levels all created on the Amiga?
As far as I'm aware, the entire game was created using
Deluxe Paint on the Amiga. The DMA team used this program for creating graphics and animations, and based their level editor on its architecture. Since Lemmings was released in 1991, it's highly likely that the team would have been using either an A500 or A3000 series Amiga, but I can't say for sure.
The level editor was never ported, but still exists on Mike Dailly's old Amiga (probably how he got the videos for the conference); something he's also confirmed in interviews.
The youtube video shows that the Amiga editor uses the hardware to show high resolution text under the main low resolution game area, which would not have been possible on a contemporary PC.
Absolutely - the Amiga was way ahead of its time and one of the most powerful machines at the time. At a time when 16 bit was the standard (particularly for games consoles), the Amiga was rocking 32 bit and doing so impressively. Sure, it had slow loading times but this could be sped up using turbo drives as well as upgraded ram and processors, much like modern PCs. Many developers favoured it for its ability to handle large, complex games with highly detailed graphics and extensive colour schemes.
I'm pretty sure that Lemmings
is "high resolution" on the Amiga, so perhaps the entire screen was in fact running at the same resolution. I'm not certain of that, though...