Welcome.
Initially, I would recommend just buying projectiles (balls). Later you'll get into casting your own, for now, just buy a couple hundred balls.
I'd recommend a brass powder flask, and a brass powder measure. When bench shooting, leave the flask behind you on the rifle rack...if when firing, a spark were to find its way into the flask on the bench beside you that would equate to a bad day...read, hand grenade detonating next to your head. No bueno.
With rifle, ball and powder out of the way, you'll also need patch and lube. I'd recommend 10 thou "pillow ticking" and commercially available "bore butter". The lubricant eases the ball and patch down the barrel and it also helps with swabbing out carbon, keeps it soft. Many guys also eventually make their own patch lube out of a concoction of beeswax, tallow, vegetable oils, etc... but initially, just buy a tube of BB, it's good stuff.
Just about anything can be used as a patch, but in order to keep a consistency of the load is why I recommend the 10 thou. pillow ticking.
If your deerstalker is a flinter, you'll need flints and priming powder, if it's a caplock...you'll need percussion caps...and you're off and shooting!
To load, aside from your ram rod, you'll need a short ball starter (maybe not a "need" but it certainly makes things easier). Some recommended rod attachments would be a ball screw (for when you dryball the gun...you will dryball the gun.), a worm, and a patch eye.
Do not put a brush down your bore...you'll never get it back out. If you absolutely must, and you really shouldn't, need to scrub the rifling, use a tornado brush as it's bi-directional. A copper brush is not.
wishing you tight groups!