beagle1

if the Canon 7D seems "huge" then chances are the other DSLR models will seem large.  If you have small hands and like smaller size cameras look at the mirror-less options like the NEX, EOS-M, etc.

nice having "L" glass - just hard on the wallet !

Don't put a 2x teleconverter on the 100-400 !  teleconverters /extenders even the 1.4 degrade image quality and affect AF and are really meant to be used with primes like the 300mm, 400mm, 500mm ,...

I don't think there is a difference except cosmetic changes to the outside (rubber grips, different focus ring)

there pics are pretty decent and I won't add to the comments other than they were all at 50mm which I presume you took with the $50 "nifty fifty" lens.  Using another lens (longer or wider focal...

the Canon T5i might be best for video but for stills I would pick the 60D http://www.popphoto.com/gear/2011/01/lab-test-canon-60d

for weddings I would pick the 6D or 5D2 over the 85 1.2 (but the 85 1.2 II is a very nice lens!)

there's not a lot of Canon EF-M lens - the 18-55IS and the 22mm "pancake" STM but with an adapter all of the other Canon lens will work.

my mistake, I was thinking of another (crop) lens.  which are usually 18mm

the 24-105 is more of a full frame "walk around" lens.  it's good but you might miss the wider focal length and larger aperture of the 24-70 2.8

for indoor low light without a flash look at primes like the 28mm 1.8, Canon 35 f2, Sigma 30mm 1.4, etc.  But many indoor shots can look nice with a flash

I'd still get at a minimum a large aperture lens like the 50mm 1.8 - it's only $50 !

if money is no impediment - Canon 1Dx or Canon 5D mkIII  with a nice set of L lens like the 85mm 1.2 and 70-200 2.8 II    or maybe a 50mm 1.2 or even 50mm 1.0 and 100mm 2.8 L or a 35 1.4 L top it...

taking a DSLR would help and a large aperture lens would help even more for night time pics (along with the flash) -  cheapest is the 50mm 1.8 ($50 used) or Sigma 30mm 1.4 (around $250) or Canon...

like others have said, you had all the wrong settings for that low light concert shot - f16 ????? for low light shots you want a larger aperture (smaller f number) and that lens is never going to...

the 55-250IS is almost as good as the 70-300 and on sale for $150 (used copies go for $100)

check out the simulator programs e.g. http://www.canonoutsideofauto.ca/play/

I agree, Canon will have the better image quality but there are other features so go to a store, and handle them, take your own  SD card and save RAW + jpg for viewing later.  join a local...

depends on your budget but the Canon 18-135 STM is good, for $150 the Canon 55-250IS is also a good value,  for f2.8 zooms the Sigma 17-50 2.8 gets good ratings

for the "nifty fifty" it's probably price.  many do not need image stabilization in the shorter focal ranges so why add considerable cost to a $50 lens