The advantage is that you will always have a supply of bullets (as long as you can find scrap lead).
In addition to some means of melting and casting, you will also have to find some way to size and lubricate the bullets that you plan to load in metallic cartridges. You might want to look at LEE's tumble lube design for simplicity....I've never used it, but it works for some folks.
Like Adam said, get the Lyman book on casting....very informative and gives the history of casting as well as a lot of the science behind it.
My suggestion would be to go with your muzzleloading projectiles first; those most likely would be the simplest to cast, don't require sizing, and lubing is basically bore butter or whatever you use for a patch lube. Also, it's a lot easier to just cast pure lead to start than trying to figure out alloys, ect (all that will come later).
Probably the biggest problem to casting to overcome? finding a source of scrap lead....with all the "bad" things that lead does to our society, it's getting harder and harder to find cheap sources of scrap lead......wheel weights are increasingly being made out of other materials and when was the last time a printer used linotype? Everything is printed off the computer anymore!
