After looking at that chart and seeing that bushmaster and colt pretty much own the market is it safe to assume the lifetime warranty most likely would not be needed?
On a Colt or Bushmaster product? Both companies occasionally produce lemons just like everyone else; so I wouldn't let it sit in the box unshot for a year; but if you give it a good test run (make sure and get it hot by firing several mags back to back - heat is a major enemy of reliable AR function) and you don't discover any problems, then chances are very good you will never have any problems with it.
If it works then, then it will pretty much continue to work for the rest of its life assuming you don't modify it until it malfunctions (which would void most warranties anyway).
With the 2 manufacturers listed above having most of the market I would assume parts are plentiful....or are most all parts interchangable such as trigger mechanism's?
Parts are quite plentiful. In fact, several different companies may sell parts made by the same subcontractor. ARs are designed to swap parts from one to the other without affecting function (assuming the parts are in-spec to begin with - which is not always the case). You aren't even limited to Colt or Bushmaster parts - you can use Bushmaster parts in a Colt and Armalite parts in a Bushmaster, etc.
This can also be a negative since few parts are marked. You can have a Bushmaster marked upper, lower and barrel and have the receivers filled with cheap, out-of-spec military reject parts that somebody slapped together from a kit. That is why it is sometimes a good idea to buy from a reputable dealer if you can.
I really do want a muzzle brake
Just be sure you realize that muzzle brakes work by redirecting the escaping gases - usually by redirecting them at the shooter or bystanders. This can make them appear louder to both the shooter and bystanders. The mini Y-comp is particularly reviled for this.
the barrels on the 6400....is it a 14.5" or a 16" with brake?
The 6400C definitely has a permanently attached muzzle brake. Colt lists it as 16" but doesn't say whether that includes the muzzle device or not. If it does, then it is likely 14.5" of actual barrel + muzzle device.
Bart is known to have a tidbit or two of useful info from time to time.
You know what they say about blind pigs and acorns