Eh, why not
I'll go through this set for as many challenges as I can. Since it's so short, that shouldn't take too long; only Level 5 will be annoying.
(All my results are from playing the set in NeoLemmix, though I imagine DOS results will be very similar for most of these.)
Max saved: 50/50, 50/50, 90/100, 74/75, 10/10
Skills you can't live without: 1 - none
2 - 1 builder. It's easily solved with builders/bashers/diggers only. Diggers can be eliminated by holding the crowd between blockers, and mining down before the zapper trap. Bashers can be eliminated by building over everything and mining down at the end. For 1 builder, go under the water and use interrupted bashers to get back up. It's not possible with no builders because of the gap after the zapper trap.
3 - 1 bomber, 2 blockers
4 - 1 blocker, 7 builders. Either the bomber or another builder can be used to release the crowd.
5 - Solvable with builders only until the very end, and then you can choose any destructive skill to get through the "2", so only builders are necessary. Finding a minimum number would be a pain, though.
Skills you need for max%: Level 2 seems to need 2 builders now, although I'm not convinced 1 is impossible.
Undamaged: 1, 4
Skills to one lemming: (1), 2, 5
One skill per lemming: (1), 2, 3
Skills to lemmings facing one direction: (1), 2R, 3R, 5R
Don't turn around: 1, 2, 5
Min skills: 0, 8, 3, 9, no idea
Level 2 with 8 is only just possible!
Min skills for max%: 0, 12, 3, 9, don't know
Min skill types: 0, 2, 2, 2, 2. Builders/miners works for Level 2, the others are obvious. (Level 5 is
not possible with builders only and the nuke; there aren't enough lemmings to break through.)
Min time: Level 1 - 0:23.47
Level 2 - Under 2 minutes
Level 3 - Under 2 minutes
Level 4 - Under 2:30
Level 5 - My best time is 4:31.29. Would have been nice to squeeze under 4:30, but this is an annoying level and I don't feel like redoing it.