A trill is just a rapid series of hammer-on/pull-off on two note. I think that they're kinda useless for anything except actual applied trills, but they might help you with thinking "fast" while playing. For example, a lot of the speed alt-pick runs I play use sextuplets (six notes per beat). Trills may or may not help you be able to process high-speed rhythm. That guy is an Iron Maiden fan, and they use a lot of trills, so that might be why he recommended it.
You should listen to different music. Right now, you are listening to well-known and accessible bands, which is fine, but if you want some better guitar inspiration, listen to some more technical prog or metal.
Also, why did you say that you know sweep picking, but then as if it's a good technique to learn next? If you don't know it, it is worth learning because you can use it in many soloing situations, even if you don't use it for traditional arpeggios.
To get better at timing, practice songs with no backing track, only a metronome. That will help a lot.
Shrink the spending on defense and put it towards education, I'd be pretty happy with the chart.
You know all that money we spend on the military ever year - trillions of dollars? Instead, if we use this money to feed and clothe the poor of this world, which it would do many times over, then we can explore space, inner and outer, together, as one race.
It's not possible. You can downtune to d-standard, or if you are already in drop-d, to drop-c, but you cannot change the pitch of one string. How the hell should guitar rig know what string you are playing on?
I hate when people display their political agenda on the ass-end of their car. That really pisses me off, and you can usually count on the conservatives driving too slowly and the liberals driving like dumbasses.
You just need to practice breath control and allotting all of your breath to the growl so that it achieves it's maximum potential (lolcheesy). If you get the technique down, you won't need to cup the mic. Muhammed Suiçmez from Necrophagist can get very low growls while playing rhythm guitar.
"Exhaling" is part of the breathing process, specifically: breathing out. If you know how to do false-chord growls (not vocal-fry screams, that's a different technique) than you should be able to hit the lows you want as long as you practice and use proper mouth shapes. If you think your lows sound too distorted, try making sure that you don't keep saliva and phlegm in the back of your throat, as that contributes to vocal distortion. If you want more distortion, do the opposite.
Oh, in that case, all you need to do is curl your tongue and have it touch or almost touch the roof of your mouth at the hard pallet while forming and O shape with your mouth, and the rest will come with simply practicing your lower range.
You're doing it completely wrong is it hurts. I'm still trying to learn myself. I recommend reading the growling thread. Also, why would you want to sound like the Whitechapel guy? He has a small range and little creativity, from what I've heard.