Hey There! New Audacity user here. Having trouble getting a good initial recording volume with my guitar - it is modified with some good humbuckers, I’ve experimented with all toggle positions, volume and tone control. I am using a 1st gen Focusrite Scarlett 2i2 interface. I have experimented with and without a direct box - ground /lift options, db options. The channel on the Scarlett keeps going into the red well before I hit the ideal -6 to 0db range on the Audacity Input/Output meters, no matter what I try. Suggestions?
Try an “amp sim” plug-in (an amplifier & cabinet simulator). (Not all 3rd-party plug-ins are compatible with Audacity,)
Or, you can try the Limiter effect (with make-up gain). Or there is a Saturation effect or some other distortion effects.
The problem is… A guitar by itself is very dynamic. It has high peaks that don’t necessarily “sound loud” with a much lower average level which correlates more with perceived loudness. A lot of acoustic instruments are also highly-dynamic and an electric guitar without an amplifier is similar (in that way) to an acoustic guitar.
Guitar amplifiers are designed to “saturate” and “soft clip” and distort in a “pleasing way” when over-driven. The saturation creates added harmonics and you get a “dense” and “constantly loud” sound. A saturated 10W guitar amplifier will probably be “too loud” in your living room or bedroom.
Tubes have a tendency to soft-clip and tube guitar amps are popular. It’s not the only way to get that sound and tube amplifiers can be made to sound “clean” until they hard-clip like a solid state amp. Or a solid state guitar amp can sound like a tube amp, but you’ll never pry a guitar player’s favorite tube amp or favorite guitar from their hands! 
Commercial recordings have additional compression and limiting to “win” The Loudness War. …And then the streaming services apply loudness normalization to bring the volume down make everything about the same loudness so you don’t get much song-to-song variation.
Oh… there’s a “quirk” if you are recording in mono from a stereo interface. The volume gets cut in half (-6dB) so both channels on the interface can go to 0dB, but when the inputs are mixed to mono it doesn’t go over 0dB. If you’re only using one input you won’t get over -6dB.
That won’t happen if you record in stereo but you’ll get one silent channel and you’ll have to deal with that.
Recording levels aren’t critical unless you try to go over 0dB and clip. You can boost later after recording.
Nothing bad happens when you get close to 0dB but pros typically record around -12 to -18dB, leaving plenty of headroom.
Unless you like the sound of over-driving the interface. Some hard clipping may actually sound good on the guitar, although you generally should avoid it on a “complete song” with other instruments and vocals, etc.
But you can get hard-clipping with the Limiter (depending on the settings) and that way you’re not stuck with the irreversible clipping that you get if you over-drive your interface.