So, was the voidsphere just an area of space that was void of everything or was it a solid that was hard to detect with sensors?
It basically "didn't exist by any form of logic; but there it was". It was just visibly
there, but scientifically wasn't. The Doctor himself confirmed that it shouldn't have existed; and that it was theoretically impossible.
Dalek-made, so it's likely to actually be impossible, but we all know what the Dalek reply to impossible is... "Oh fuck that, I don't believe in impossible"
That wouldn't entirely be out of the realm of real life possibility, since there are software programs that companies can put into their computers to track what their employees are doing on them and remote access to computers that's wireless exists.
A woman was typing on an unsaved file; and then someone deleted everything she had written, because it had contained classified information. (This is after giving her amnesia pills that would essentially erase her memory of Torchwood during her sleep; pretty nifty invention)
The borg do know and have reliable time travel technology, whch would have to include good temporal sensors, given when they went to in FC.
But not as good as the Daleks ;)
The Daleks have similar level to the Timelords when it comes to temporal technology, and they don't suffer from massive shipboard malfunctions (like in FC) when time travel is invoked. But this is basically because to serve as a longtime enemy of the Doctor and remain at full strength, you must at least have some form of time travel capability.
Can individual Daleks travel through time without a time pod?
Black Daleks can, and perhaps the other Daleks that were in the Cult of Skaro can as well. The Black Dalek used an "Emergency Temporal Shift" (which could mean that it was just a random burst of temporal travel that ended up dumping it in a dustbin some five years ago; or that normal controlled travel would require some warmup time.)
Is their energy draining abilities limited to just electricity and temporal energy or are they more free range? Since we don't know how much power a cube could put out, they could try overloading each Dalek's absorption abilities, but I can't be sure.
Well they were considered a threat to the Timelords, so they could possibly have extended it to whatever the Timelords used for energy in the midst of electricity. I would say that a cube wouldn't exactly overload a Dalek if they had some measure of just pumping it back out into the air again, though. Maybe "absorb and fire gun" repeatedly in various sections.
The borg have also shown shield energy draining abilities, too, for ships, but I don't know if they can project it inside a cube.
Or even if Dalek shields are advanced enough to ignore it. In ship-to-ship combat, it probably wouldn't be a question worth answering since Dalek ships are comparable on at least some level to Death Stars, but faster, probably stronger and smaller. They did perform a 'base-delta-zero' of Earth during Parting of the Ways.
We also know that they can open up singularities that lead into parallel realities, but we don't know how small they could make them or even if they could do it on the inside of a cube.
I think it's best if they don't anyway; it could do just as much damage to themselves as it does to the Daleks.