Jeff hate bad sarcasm.
JEFF SMASH!
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Sorry, the last meds didn't work, so I'm off completely until something new pops up. You couldn't tell, right? I'm sure you couldn't. In the meantime...
1: 57 or i5 is great to start with. 421s are also popular, especially mixed with a 57. I personally like to yank the transformer out of my 57s, to get rid of a lot of that nasal peak, add in lows and highs, and make the response seem less... well, badger-up-the-twat. I'm currently just using the i5 because it's so easy to get what I need out of it and I'm not sitting still for five minutes at a time these days.
2: Depends on the mic and what we're going for. With a 57 it might seem necessary to get into proximity-range zone, but I've never had that problem with an i5. I don't consider distance from the cab, as different cabs will have different speaker positions, but I'd try to get as close as possible without things getting too boomy and unclear. I use middy sounds and as a result don't need to worry as much about that sort of thing as some of the scooped-to-fuck-and-back lot, but with any tone proximity effect is something to be very well aware of.
3: Same as above - mic, intended sound, how much tinkering I'm in the mood for, et cetera. Right now, from the looks of it, my mic is fairly close to the joint between dustcap and cone and tilted slightly out. I can get away with different things than most, though, because I don't go for a very gainy sound - my gain is pretty much set to be a little light for Van Halen with a 'normal' picking attack, and I beat the fuck out of the strings to get things into the higher gears, never really getting anything with as much buzz or sizzle as the average metal band. I like having a lot of 'bounce' in my tone, so I can get closer to the dustcap and have a brighter sound going in, and as a result I can't say anything more than 'sit there for just about fucking forever until you find the right spot' - I could have sworn we just went over this a few threads down, look through the list and you'll find more detail and some real-world examples.
4: One very important factor in my sound is a two-foot-tall stuffed panda bear that sits next to my amplifier and guards it from the elves. They're sneaky buggers, they are. Also helpful is a tight performance, a well-set-up guitar, and above all knowing what the mix needs and not what will sound good on its own.
Jef