As someone that plays 1.C4 as white and uses the Botvinnik setup, what causes me the most trouble is a symmetrical setup. I usually have very good results even against 1800+ players, but the symmetrical system usually give me the most trouble.
What to play against 1. c4...
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c4 the English open, its a good one. I would suggest e5 so you can attack d4 sqaure or either Nc6 or Nf6. Whatever you choose you have to claim your middle board.
c6 is not a bad response at all, all you have to do is to study the lines after 2.e4 in the Caro, which you might already know. any other response can just give you a very natural game. you will get some Slavs using this move order, but beware, as English players might try 2. g3, which is likely to lead you to something you don't like... like: 1.c4-c6 2.g3-d5 3.Nf3!?\Bg2!? or 3.b3!? and stuff like that.
ScottM84> Considering the fact that playing 1... c6 has the potential to transpose into a Slav I've considered that, but is there anything I should consider before adopting that?
After 1...c6, White's main options are to transpose into a Slav (2.d4), Caro-Kann (2.e4) or Reti (2.Nf3). If both the Slav and Caro-Kann are already in your repertoire then 1...c6 is probably your best option. It would be kinda silly for you to learn all the complex theory behind either 1...e5 or 1...c5 when you can so easily sidestep it.
I play 1. ... c6 or 1. ... e5, usually e5 since c6 almost always leads to a queens-pawn type game & English games are usually more interesting. 
CPawn> As someone that plays 1.C4 as white and uses the Botvinnik setup, what causes me the most trouble is a symmetrical setup.
The Botvinnik setup often leads to long positional struggles. If that's not to your taste, instead of going for d2-d3 ala the Botvinnik, break the symmetry with an early d2-d4, and the position opens again and perhaps you're happier.
I'm looking for some suggestions as to what would be a good defense to play against 1. c4. My main defense to 1. e4 is the Caro-Kann with an occasional French, and I usually play the Slav against 1. d4, my main secondary defenses being the QGD, and every now and then a Queen's Indian.
Considering the fact that playing 1... c6 has the potential to transpose into a Slav I've considered that, but is there anything I should consider before adopting that?
Just to give an idea of my level of play, I've been improving fairly rapidly over the last few months. Five or six months ago, I was playing at a 1300-1400 level against Chessmaster, but recently, I've been playing at a level of 1700 or so.
With all that in mind, does anyone have any recommendations?
Thanks in advance!