What we call "magenta" is the sensation of both red and blue color-sensitive cells in the eye being excited at the same time. There's no single wavelength that produces this effect (unlike e.g. yellow). The closes you can get is violet, which looks faint to the eye.

A rainbow gives you both red and blue; mute everything else, and you'll get magenta. That's what magenta pigments do when illuminated by white light (which is a rainbow scrambled).

Not very! This is on the "line of purples".

Here's a nice visualization of color perception (there are more modern ones, but we used the 1931 color space when I was working in the field). The horseshoe shape on the outside is the single wavelength colors.

https://en.wikipedia.org/wiki/CIE_1931_color_space