Yes, take the data as raw as possible to leave as much headroom as possible for corrections.
No, in vuescan just scan to “raw” tiff as RGBA such that the infrared channel is saved. For best results, don’t apply the infrared correction as vuescans own inpainting is not too good. In the thread Scanned image scratch removal with “ICE” are lots of comparisons, and out of the thread evolved a g’mic script that does correction based on the RGBA data.
Depends if it is the gain of the amplifier or the light source that is controlled with it. If it’s the light source, it should be safe to adapt. If not, it depends, I have no experience with this particular scanner.
The (mini-) lab-grade scanners of fujifilm and noritsu do exactly this, but are limited in resolution and extremely expensive. However, they illuminate independently with r, g, b, and IR LEDs which is reported to be ideal for negatives as it deals with the orange mask of the film in a smart way. I want to try this myself one day with a camera setup, but there’s so little time …
For kodachrome, however, it is reported that IR does not work anyway, for the other film types it should work well.