These kinds of things are taken into account during aircraft design so that they are not a big issue:
The weapons are already generally lined up with the CG, so firing them off does not appreciably change the CG (that I can tell).
The fuel tanks are arranged in such a way that the CG does not change appreciably as fuel drains out of them.
The total amount of hydraulic fluid on the aircraft is not heavy enough to cause a noticeable shift in CG. Besides, if you lose all of your hydraulic fluid, you have much larger concerns.
The aircraft isn't really watertight, so if there is hole big enough for fuel to leak, it will leak out of the aircraft, not redistribute itself around the aircraft.
The fuel tanks have baffles in them to prevent sloshing that would alter the CG of the aircraft.
To try to answer your third question, using normal loading, there isn't any way to get the Ka-50 out of CG limits. The only possible thing I can think of would be to fill one of the fuel tanks (aft or forward) and leave the other one empty, but even then I am not sure if that would be sufficient to throw the aircraft out of CG limits.
I think the only way to really get the aircraft out of CG would be to have part of it shot off. ;)