Okay, my thoughts on level ordering, and possibly some other random comments:
(Gentle 8-10) Snuggle Up To A Lemming presents the fewest hazards, and should come first. Get A Little Extra Help also presents very few hazards, but more importantly, it feels more different from the other two than they do from each other, so it makes sense to seperate them with it. While there's no denying Downwardly Mobile Lemming is still pretty low on hazards, there are a few more, and they're not quite as easy to avoid - yes, still very easy, but not as easy.
(Gentle 11-12) A Block From Home is actually kinda tricky, especially the bit right at the start. Keep Your Hair On Mr Lemming introduces a new mechanic, but is otherwise a very straightforward level. I thus suggest swapping these two.
(Gentle 13) I'd move Where Do You See Lemmings a bit further back, due to the tight save requirement. Somewhere around 20 should work well.
(Gentle 23-24) Lemmings In The Attic, on the other hand, should be a little bit earlier, probably close to (but before) Rainbow Island. Darkness Of The Royal Family should be even earlier than Lemmings In The Attic; while it does only give 5 of most skills, it gives 10 builders, and 5 of each skill is more than enough here.
(Quirky 4) I feel this is way too early for Dolly Dimple. I'd actually consider this to be a fairly hard level, definitely worthy of being in a later rank than Quirky.
(Quirky 6) Postcard From Lemmingland, it's in the right rank but I think it should be later. Keep in mind this level was a major roadblock for many players on their first playthrough.
(Quirky 9) With A Little Help From My Lem, if I'm not mistaken, requires one to be quite precise. It originates from the NES version which operates on a tile-basis even for physics, so precision is not an issue there. While the position is fine, I think some adjustments to address this may be needed.
(Quirky 13) Across The Gap; I remember struggling a lot with this one when I first encountered it. However, looking at it now I'm not sure how I found it hard. Anyone else feel this way about this one? If so, we might want to consider moving it to a later position.
(Quirky 21) The Crankshaft; I think this level could go a bit earlier. Somewhere near Postcard From Lemmingland, but not right before or after it feels right, I think?
(Quirky 22) Compression Method 1; position is fine but the traps should either have no overwrite on, or be moved up one pixel (so the top of the trigger platform is at the top of the blocks). I personally would prefer the no overwrite approach.
(Zany 5) I think the trick from Let's Get Together, unless there's another solution I'm not aware of, is a bit too advanced for this position. It should probably go into the next rank.
(Zany 7) The Run Around belongs in early Quirky at best, I think. Don't get me wrong, it's a really fun level, but it's not hard at all.
(Zany 13) Let's Go Camping; based off the "remove the digger" fix, this is WAY too hard for this position and belongs near the end of the game. GREAT level though!
(Zany 17) Mr Lemming Lives Next Door feels like it should be a bit earlier; maybe near the start of Zany, or even late Quirky.
(Zany 19) Tunnel Vision is too easy for its position; this one definitely belongs in Quirky.
(Zany 29-30) I think that Temple Of Love feels better as a rank ender than The North Poles.
(Manic 7) Emmings! (No L) is a bit easy for this position, I think. Somewhere around mid-Zany might work?
(Manic 9) Rocky Road, I get the impression falling off the rocks to the right of the entrance should land in the trap trigger area? Might need an adjustment for this. Even with this taken into account, it seems too easy for the position; it's basically just a worker lemming level that requires you to be somewhat conservative of skills.
I'll go over the rest of the pack another time, I think.