Sounds like you've already gotten the advice you need but I'll throw a few comments out there anyway:
-You're thinking backwards about how the vents work. Closing the vents doesnt help keep in. Open vents = more air = more fire/heat.
-As noted the water in the pan is not necessary (and might contribute to the lack of bark). Wrapping in foil definitely will kill that bark.
-Snake looks pretty small....how much of that charcoal got used up during the cook? I tend to aim for 75% of a complete circle for a 3-4 hour cook (but lots of things can affect this like the weather, etc).
-There are no set rules for this. If I aim for 250 degrees I'd be happy anywhere from as low as 200-225 to as high as 350. If your kettle was running cooler than you wanted, then you could have increased the cook time accordingly. Conversely, if it ran hot, they'd have cooked for a shorter period of time. Biggest trick is to just be aware if/when you dont hit your target temp (or surpass it) and changing your cook time as needed.
-If the ribs were tough thats the clue you probably could have left them on longer. With something like ribs, I'd rather cook it longer at a lower temp than try to speed through it at higher temps. I've tried hot and fast ribs and dont enjoy them quite as much (could be a mental thing though too as I enjoy the slower process!).