A. The theoretical effect of higher metal concentration is an increased tendency for plating thickness to track the geometry of the current flux--that is worse thickness distribution.
B. But faster plating.

1. I think the function of the boric acid is the same as in a nickel bath--as a pH buffer to offset the tendency of the bath to rise in pH as water hydrolizes into hydrogen bubbles and hydroxyl ion (alkali). I don't know how effective ammonium chloride is in this regard or if it serves a different function.
2. In theory, raising the temperature has the same effects described above under raising the metal concentration. But in actuality, brighteners degrade faster at higher temperatures; I believe that proprietary brighteners for ammonium chloride baths can take 110 or more, while those for potassium chloride baths are much more limited.
3. Voltage depends on anode to cathode distance, but 6 to 12 volts is pretty common.
4. Sounds right on target, but the math can be checked on page 791 of the Metal Finishing Guidebook.

 
Ted Mooney, P.E.
Finishing.com Inc. - Brick, NJ