Here are some answers:
1. If there is a brown or black ppt at the bottom there may be 2 causes. One is not enough ammonia and the other is that the Silver Nitrate is old or low quality. If adding more ammonia does not clear up the brown ppt. then the Silver Nitrate is not very good.
2. As temperature goes up, crystal size, fog and speed generally go up. You can offset this by shorter hold times at a given temperature in some cases. As temperature goes down, the crystals go down in size, fog and speed decrease.
3. I use 4 deg C for my wash. Volume generally goes up. You can add some 20% gelatin to this to stiffen it up, but you usually have to coat a tad more emulsion per unit area to offset the dilution.
Gelatin can break down at any temperature if the pH is too high or low and it can break down at any temperature with a long enough hold time. I try to stay below 80 C and preferrably at or below 60 C for these makes. I try to keep holds at or below 1 hour and the Ammonia digest is probably not alkaline enough to cause a probem with these conditions.