Bigbore:
1, you will need to clean your bore often using BP, some rifle actions are easier but some 'after market' sights will make that impossible (from breech end) - I know a few ranges won't allow access to clean from the muzzle during shoots
Yep, I do that now, about every 10 shots. I'm fortunate to have a pristine bore in my lightly used trapdoor.
2, if you use the taller say 1000 yard sights, then doubtful you will be able to adjust them lower than 200 without removing the fitted rear barrel sight on some rifles just to see the front sight - that can prove difficult for hunting or shorter distance etc...so it may mean a rifle set for one purpose only...which seems what you are after anyway from your post
I have a set of 4 custom trapdoor front sights that a gunsmith/machinst buddy made me, made from titanium and using an EDM machine. You can PM me if you have a TD and are interested ($35 for set of 4) This really improved my long distance accuracy with the buffington!
3, load development is essential because most of those cals you mention are easily capable along with others but unless it's enjoyable for you to use - you'll quickly lose interest and it will become a safe queen
With the help of member Sharps45-90 (Member here and another forum), I've developed some great accurate loads in both 405 and 525 gr boolits!
4, visit some shoots, ask questions and see for yourself what people use, most will let you have a go of theirs once you chat....well, unless they use original Sharps.....best check their facial hair first before you ask...., just in case :grin:
Tough to find any of these in WA state that are BPCR :(
5, don't expect to neuter gnats first up at 1000 yards....it will take time - but then that's the fun bit.....
Can't wait! I may be traveling with my TD this summer and practice at my brother's ranch in Ennis, MT!