The recoil really depends on a lot of things- gun design, weight, weight of powder charge, weight of bullet, etc. I have a .45 CVA that is lighter than the Kodiak, so the recoil is worse. With a 200 grain bullet and 100 grains of loose 777 FFFG (about 2000 fps) I would say the level of recoil is close to a .30-06, but with more of a "push" than a sharp kick. Like Cauygad said, make sure you get a scope with plenty of eye relief- I learned that one the hard way.

If the recoil's a bit much, you can always back off the powder charge a bit. With 80 grains of 777 I consider the recoil to be very tolerable- on the level of a 20 gauge shotgun or so. No muzzleloader I've ever shot had recoil anywhere near that of a 12 gauge slug.

With the .45 you're going to have less bullet selection than with the .50, so you have to be creative. Lane Nebraska probably has the most experience with .45's of anyone I know on this forum- he may impart his wisdom. A good place to start is to get some .40 cal XTP's - either the 200 or 180 grainers. The .40 cal 200 grain SST's/Shockwaves are a good bet too. Get some loose 777 or BH209 and start off at 80 grains and work your way up in 5 grain increments until you find what your rifle likes. For example, my rifle loves 95 grains of 777 - anything less or more, and the groups open up. But each rifle is different...