If you like the rifle, buy it. Figure out what you want to load it with and run with it.
Things to consider:
1) If you need to use BP, and you can trust me on this, accuracy will not suffer and if inclined to hunt with it, soft lead/tin alloy will drop stuff stone dead.
2) Smokeless? Load it and figure it out.
The .45-70, with heavy bullets will abuse your shoulder a bit, matters not what powder you use.
Couple of targets:
.38-55, offhand at 100 yards at a shooting match. Load was BP and a 300 gr cast bullet. The gun is designed for offhand shooting and has a scope.
.45-70, 5 shots, elbow rest and tang sight at 100 yards. Duplex max load, 530 gr cast bullet. Friend of mine calls the gun "Thumper"....for good reason. Weighs a bit over 11#, fits me quite well and does not charge for bruised shoulders.
Both rifles are Highwalls.