RE: Arrows and field tips
The size of the arrow depends on your set up. Different draw lengths, draw weights and bow models require different arrows to shoot well.
As far as size, I believe most carbons are 19 or 20/64's in diameter. The most common arrow sizes are usually 20 or 21 series I think. I don't sell arrows for a living though so I could be off.
Worry about what arrows you need first, then get the right size tips. If can't get the right size tip, try and get one smaller than the shaft vrs larger. A tip that is larger than the shaft will be hard to get out of some targets. Some ranges will not even let you use them because it ruins the target.
Paul