I've come to the conclusion that there isn't any advantage to using roundballs in place of normal bullets when it comes to loading up .45 Colt. I don't cast my own so my statement is based on the cost of purchased supplies like bullets and roundballs. I'm cheap too!
I decided that for purchased supplies BigLube bullets are easier and just as cheap as Hornady roundballs. The 150 grain BigLube bullet (next to the roundball in the photo) is the closest thing you'll find to get similar type performance to a roundball type load.
Be careful when referring to Pyrodex as BP. Pyrodex is not BP. It is a substitute for BP. While in some ways it has "similar" characteristics to BP in other areas it does not. You can read more about the differences
here. It would appear that Pyrodex is harder to ignite than BP. You probably don't need magnum primers but then again you might find the performance is better with magnum primers. BP is easy to ignite and does not need magnum primers. Actually, I see that you didn't refer to Pyrodex as BP...my bad.
As far as the crimp goes you will probably find it takes more of a crimp to hold that roundball in place. You can probably see that in my photo. The last thing you want is for your roundballs to get jarred lose under recoil and end up with multiple discharges at the same time. Crimping just enough to prevent the roundball from "rolling out" is not good enough for government work.
As pointed out previously, there is a disadvantage of using roundballs in that there's no easy way to deal with lube. Personally, I think putting lube on top of a cartridge is somewhat silly. So your other choice would be to use a lubed wad or grease cookie under the roundball. You could do that but I'd recommend a vegetable wad (0.030) between the powder and the lube/roundball.
You were correct in your selection of 0.454 roundball. 0.452 would be great but who makes those?
For loading equipment I used my Lee single stage press and Lee .45 Colt dies. I should point out that to seat the bullet I generally tap the roundball in with a rubber mallet to the right depth. The reason for this is that the 0.454 roundball is a little bit larger than the 0.452 Lee dies were made for. Thus, it is possible for the roundball to get stuck in the bullet seating die.
In summary, here are the disadvantages to using a roundball.
1. No easy way to lube.
2. Can not easily use the Lee die to seat the ball.
3. As purchased not cheaper than a BigLube bullet that comes pre-lubed.
4. Heavy crimp required to guarantee it doesn't jar lose under recoil.