The water must fit within a 5 foot cube, per the first sentence of the spell description. it's not 125 cubic feet in any shape, it's a bounding box.

This only determines the water you affect with the spell. It does not say anything about the spell effects being limited to this 5-foot cube, only the water you can cast the spell upon. You can stretch it out into ribbons if you like, since that's a simple shape permitted by the second bullet.

You can't take it with you. “Animate” doesn't cover moving it (think of animation as just a succession of new shapings in-place), and there is an explicit limit of 5 feet in the first bullet for how far you can move the water.

It can't affect ice or snow, only the colloquial, common, non-chemistry meaning of “water” that means the liquid phase. You can see this colloquial meaning used in the last bullet where it talks about how you can “freeze the water”. (Wouldn't make much sense to substitute “ice” into that bullet point, would it?)

Not as much protection as you'd think.

Try this at home - get a shovel, and try to pile "loose earth" into the shape you've described (3ft tall, 2ft deep wall). It will immediately fall down into a pile. The angle of repose of soil is 30-45 degrees. In your configuration (2ft diameter base) the pile needs to have an angle of repose of 75 degrees. So the entire thing flops over to about half its height. The soil from the sides of the hole is also falling inwards, filling up your hole, probably reducing the amount of cover from the hole by half as well. If you're unlucky, the soil from the wall will fall backwards into your hole and reduce the depth even further. It would look more like this:

|      OO

|   OOOOOOO

XXXXXXXXXXXO      XXXXXXXXXX

XXXXXXXXXXXOOO XXXXXXXXXXXXX

XXXXXXXXXXXXOXXXXXXXXXXXXXXX

If you're lucky, you'll get 3 feet of cover (partial cover) out of this. There's a reason soldiers build trenches out of packed, not loose, soil.