It is painful to play without a mouse, but you can't just switch to some other (mouse supported) version, like it's doesn't matter. Levels are not the same. It's not the same game.
Although, it's not a bad idea to switch to Sega Game Gear version (much more colorful graphics and better sound) or Sega Master System (not so good as GG in graphics and sound, but certainly better then Gameboy). Master System version is easiest to play of all 8-bit versions, because resolution is much higher then GB and GG (even higher then SNES version). So, 'window' to the level is much bigger.

No, he didn't say anything about the second edition. That's why I hesitating to bother him with these mistakes in the book.
I don't think PDF release will cost anybody anything (except the time for editing content). He is gave PDF version for free to everybody at the end of the last year, so he can just update PDF file.
Look at this link if you are interested:
https://cd32covers.blogspot.hr/2016/12/unofficial-cd32-release-more-lemmings.html

As I am not familiar with all of the ports, I can't find all possible mistakes in the book by myself. So, I don't think it's a good idea to correct just these mistakes and declare the second edition.
Jay's 'Everylemming.blogspot' was very good online place with lots of useful information about Lemmings games. Sadly it's not online anymore.
Fortunately, this forum is still very alive, and I can't think of better place to gather people willing to check content of the book and report any possible mistake. But, Jay is not here anymore... What now? If he don't want to be member of this community, I don't think we should dissect the book to the details here.

Yes, it is. There are differences between NTSC and PAL Amiga models (200 vs. 256 lines on the screen). PAL Amiga model, normally leave unused bottom of the screen when NTSC compatible game running. But, if you don't like that 'NTSC game on the PAL Amiga' look, it is possible to configure size of the WinUAE window or full screen mode for the correct aspect ratio.

There is no intro or even any tune for ONM Lemmings (as I am aware) only picture on the Amiga and Atari ST:


Amiga


Atari

And not even that for the X-mas and Holiday Lemmings.

When you finish Genesis port of the Lemmings 2 it will be great if you can make full playthrough of the Sega Master System (SMS) port. This will be the first playthrough of that port. You can play this one with the same emulator you are using for the Genesis version. Only bad thing is lack of the mouse support for the SMS version.

Yes, only SNES version works as it should, Swimmer Mango Booter just start to swim in the water and after he came out of the water is just walker (and Swimmer as it is permanent skill) again.
On the practice skill selection screen you can't select 20 of them. It's only possible to select each skill just once. But when the practice level starts there are 20 (or 99, depending of the version) of each selected skill to use.
There is a problem with selecting skills for practice on the PC (and just on the PC) "Insufficient Memory" message can occur on some skills depending on which skills are already selected. Like, some skills require more memory then others. But, the PC version is the only one where it's not necessary to select all 8 skills for the practice.

Time given for the practice levels is also not the same in all versions.
PC and FM Towns 9:00 (except Egypt 9:01, strange isn't it?)
Amiga, Atari, Archimedes 9:00 (except Egypt 9:01) but timer doesn't counting, so it's actually endless.
SNES 5:00
Mega Drive 3:00

And some more interesting facts:
SNES, Mega Drive, GB, GG and SMS do not have color inversion for the permanent skills.
Atari ST is only version without Intro animation and End animation.
SNES is only version with the background graphics on the levels (except for the Classic tribe) and only one with snowfall on the Polar tribe (simple but nice effect).
FM Towns is only one with a 'real' flame on the Jet Pack skill. Just dots on the other versions or even nothing on SNES, GB, GG and SMS.
I have already mention left and right Twisters on the Mega Drive.
And certainly plenty more details, I don't want to bother everybody with that things any more.

Not just Twister, they can do lots of things under the water. Roller, Archer, Attractor, Flame Thrower, Runner, Skier... etc.

I didn't know about that entering level priority. Checked again, paying attention to not select the first lemming for digging. I wasn't correct the first time, FM Towns is affected (not very surprising because this machine is a kind of PC).
Finally (I hope) there is assignment priority problem on this 5:
PC/DOS
FM Towns
Game Boy
Game Gear
Master System

and these 5 don't "suffer" from that at all:
Amiga
Archimedes
Atari ST
Mega Drive/Genesis
SNES

5 out of 10, so it's just half a problem. Isn't it?