All things considered and being equal between two guns the 45 caliber will be ballistically superior to the 50 caliber. With that being said, neither is a bad choice or a wrong choice and they were both serve you well as long as you experiment and practice with load development and find a load your gun the best.
Low development and practice are much more important than your choice of those two calibers.
There are still more choices for the 50 caliber whether you choose bore riders or sabots, but if you go fullbore with the 45 the number of available bullets increases dramatically.
In my Mountaineer fast twist 45 I can shoot a fullbore Fury .4505 QT style bullet at 275gr just as accurately as I can shoot the Fury 240gr QT 401 in a sabot
As for the rifle, that’s a personal choice of whichever gun fits your needs the best. My understanding is that the woodman is very light or if you’re hunting long-distance walks and hilly terrain you might want to consider the weight.
I can tell you that my Mountaineer is a joy to shoot but it is heavy although they make a lightweight model now.
If you buy a Knight and you’re going to shoot bare primers I would highly recommend having the gun shipped right to Bestill Creations (with his prior knowledge of course) and have Jeff make you a breech plug that actually fits your gun and won’t leak. Otherwise you will have problems.
I really like the CVA 45 caliber LR-MRX with a 30 inch barrel, but then for me…. I hunt from ground blinds and ladder stands & I don’t walk very far
So the bottom line is you get as many of these guns in your hands as you can to check the fit/feel and buy the one you like.
Greg