I'd say no to the lava infused loose cobble/stone bricks. Being able to pick it up really simplifies the machinery involved for cobblegens atm
On clay: I think the recipe for historic reasons could be changed to give only 1 clay ball back, it'd cost a very small fraction of people some clay maybe, but with fair warning etc it kinda feels weird to account for that person, plus its not a hard lock, just some wasted resources in a world that had an absolute overshot compared to the worlds of today.
So with that in mind, I'd like clay ore to be obtainable, for the same reasons other ore blocks are: to place next to a fortune beacon and work its magic!(once that's changed for clay in an upcoming patch)
Ice allows infinite horizontal item transport without requiring elevators. I think it's fine if an addon wants to make it obtainable, but not BTW itself.
No they don't but it's enough to let them cross the gap between one water stream ending and another one beginning. It's harder to do than vanilla because you need to get a little fancy with the screw pump setup but it is definitely possible.