A lot of what makes a muzzle loader the best is dependent on the price you want to pay. Ashland Guns inline muzzle loader is called the best by some but comes at a price of over $2500. Others consider the Accura by CVA to be the best at $600.
They are called muzzleloaders simply because the powder and bullet are loaded from the muzzle end of the gun, Here is a page from WIKIpedia that may help answer.http://en.wikipedia.org/wiki/Muzzleloader
Which type of muzzleloader may be equipped with a mechanical safety?
No
Yes
Cabella's
Cabela's or Dixie Gun Works would be your best bet, or gunborker website.
"Best" is a subjective term that depends, among other things, on your skills, intended use, pocketbook, "feel" of the weapon, etc..
That depends on the make and model.
rust
removing the breech plug
2
Unknown