1. If you want to use the dies for both the Special and Magnum cartridges, make sure the dies you buy are described as usable for both calibers. Most newer dies can be used for both, but in some cases, the crimping die in the magnum-only die set may be too long to allow crimping of the shorter cartridge. If that is the case, the die set is usually labeled for use in loading ONLY the magnum cartridge. Here is an example.
Die set for .44 Magnum or .44 Special (click link to see item): Lee Carbide 3-Die Set 44 Special 44 Remington Mag
Die set for .44 Magnum only: Lee Carbide 3-Die Set 44 Remington Mag
2. Personally, I just use a lower-power load in Magnum-length cases, and use the bullet type to show me what the intended use is for each load. For instance, if my .44 handloaded cartridge has a wadcutter or semi-wadcutter lead bullet, I know it is a low-speed or a middle-speed target load. If it has a jacketed hollowpoint bullet, I know it is a full-power hunting or personal-defense practice load. To me, it seems to be easier to find a more accurate load in the magnum-length cases, perhaps because the distance the bullet has to "jump" to the barrel is reduced.
If you take a measured amount a gunpowder intended for a .44 Special load, and just dump it into a larger .44 Magnum case, you may not get good results with the same bullet, as the larger internal size of the case changes the pressure of the load. In many cases, I have had to increase the powder charge slightly to get good accuracy and the same velocity as shown for the load in the smaller .44 Special case, but you MUST BE SURE that a small increase in the charge is still a SAFE load for that cartridge and and gun.
3. Sorry, I have no experience with the gunpowder you listed.
Good luck, and good shooting!