I got started about, oh 1990 or there abouts with an original Sharps conversion and a Trapdoor. In the following years I spent a lot of money that I shouldn't have by buying unnecessary stuff, and lower quality stuff that eventually got replaced with equipment I should have bought in the first place.
I traded the original to the owner of C. Sharps for a new high grade sporting rifle, and made my first mistake. I got all historical and wanted something unique so I got it in .40-70 Sharps Straight. Mistake. I should have gotten a .45-70 and I still advise that. Components are much easier to find. A .45-70 can reach 1,000 yards. It may not be ideal, but it can do it. But other than the extreme long range, a .45-70 can do it all.
Sights, here is a place where I wished I had listened to a couple of friends that shot BP competitively. They told me to buy MVA Soule sights, and I have them now, but I wish I'd bought those first.
Moulds , boy moulds. A good copy of the Postel bullet should serve you well. Buffalo Arms is an excellent resource. Buller alloy, don't mess around with range scrap and wheel weights, get or mix up some good, repeatable, 1/20, 1/30, or 1/40 tin to lead.
Powder, Swiss or Old Einsforde, 1 1/2 fg.
You do not need magnum primers, black ignites easily.
Buy a dedicated die for compressing the powder.
You will need wads between your powder and the bullet. I use Mike's laminated paper wads. Any quality wads will work, as will home made with a proper wad punch. Waxed milk carton will work well.
Lube, Bullshop's NASA lube or SPG. I wasted a lot of time making home made, don't bother.
Ian's advice get a copy of Mike Venturino's book is sound advice.
A delrin wiping rod is handy for wiping between shots.
A well fitting blow tube that completely fills the chamber for when you have to shoot dirty. A short blow tube will leave condensation in your chamber
and your fired case will tear in two leaving part of it in the chamber or up the bore. This is a fact!
This should give you plenty of food for thought , and some indigestion too.