A knife vise, that allows you to rotate and move the blade at different angles, is a game changer to be sure. I built my own many years ago, so I can't really help on where to buy one. Finishing abrasives come in countless varieties, and everybody has their preference, but my experience, and advice is that the backing plays a huge role in cutting efficacy. Thinner papers are nice but serious removal can be had with heavier backed abrasives.
For using them, I have several backing sticks. The first is made of steel and is for aggressively removing scratches. Next I have sticks I made from osage orange, any solid and hard wood would probably do, that I have glued eight ounce leather down one side of. The wood is for finer polishing and the leather is for the final, burnished finish. I have found that a good water based cutting fluid will get the job done quicker, due to more aggressive cutting and keeping the abrasive from loading up. Always hand finish at least one grit higher than your final finish and then step back to pull on your even, straight-lined, finish, with no nasty fish hooks.
Oh, and what Ed said about the 2x4 and C-clamp is good advice. I still have to do many of my swords this way. It gives good support and keeps that sharp point from hanging out there.
One last thing- There is production level knives, (which there is nothing wrong with), and there are high end custom pieces, of the type you get an MS rating with. Crisp, clean, lines are maintained with careful hand finishing. Scotchbrite and other flexible, quick-finish machine abrasives, work good for production level knives, but they round out, and wash away, crisp clean lines on high end custom work. For example, most folks should avoid mirror polish work if they think it is done with a buffer. A proper mirror polish is tons of handwork, down to 2000X or better, before a final light buff. Going to 600X and then laying into the buffer like crazy is not a mirror finish, it is a blade with no lines left that is covered with highly polished and smeared scratches and it really looks much worse than a clean 400X satin just done by hand.