Raven,
No one component of this makes the challenge difficult. It's the overlapping problems that makes this more adventurous.
First, there is no safe form of food gathering to start. Since anything that's dead can come back and kill dwarves, butchery, at best, must be undertaken with extreme caution and prejudice. There is very little vermin to be used in the ice for food to recover from a hunt for vermin spiral, except on the surface, where the undead roam.
Next, you have no water that's usable quickly unless you have the aquifer, which compounds the other side of the problem, how to get to the caverns. If you don't have water by mid-slate, your embark dies on a dime.
So, you've got time problems. Compound that issue with unskilled dwarves who take FOREVER to do anything. You've got two months to breach a cavern for plants and water or you have to come up with alternate methods, without using that wood you brought because you're going to need a few axes for trees.
On a number of test embarks I outright MISSED the caverns until I hit the magma sea, and that's a 2x2 stairway. You don't have time to miss, because those caverns aren't empty and your dwarves are not armed in any fashion, so usually you have to be canny about where you go in. And hope there's water if you're not using an aquifer. Wrestling training can kill your dwarves outright if they're not metal armored, so you can't let them train while they're sitting around twiddling their thumbs, either.
So, I agree in a way, there's no particular challenge directly revolving around the single pick. It's the environment you're doing it in that goes from 'eh, okay' to 'huh, how the hellll....?'
Which, to bring me to my point... the next video is up. Food, water, migrants, and the cavern search shaft has begun. See the first post or just click here:
https://www.youtube.com/watch?v=_C2EVbxVQNkEDIT: Oh, yeah, sorry guys, when I go back in for Part 2 I'll get your names in on the dwarves. This attempt was recorded while the first one was just going up on youtube and was taking a bit so I hadn't fired up the thread yet.