gain and threshold questions

[arcarsenal]

hey,
lets say i have a track with the output between 0 and -3 the whole time. would it be clipping if i raised the fader up to +6?

early on i got into alot of bad habbits that im trying to break, i.e. tracking at low levels, normalizing/gain boosts, stupid use of the fader, and other things, and im trying to start getting into good habits.

i know a few things, but im a bit confused on some.

i know to track as high as possible without clipping, not to use the gain/normalize, but lets say ive got typical drums/guitar/bass/vocals/keys, generally speaking, if you record them all fairly hot, about how low would you guys have each individual fader?

for some reason, i do all that and have my faders from only about -3 to +6, and i know somethings got to be up.

also, when people refer to common settings for dynamics [compression, gate], and they talk about the threshold being -20, wouldnt it be different for everyone, depending on how close their signal is to 0?

and also, this would help me break some more bad habits with the fader, is there a way [in the edit window faders, not mix] to display what the input signal would be AFTER i use the fader?
so if i was +6'ing everything, i could actually tell that its clipping?

thanks