Your vent on this particular smoker should always be fully open when in use...it's a smaller vent on a fairly large cabinet, so it's going to need all the venting you can give it. Adjust temp with flame only. The burner control valve has a keep warm function, if you push the knob in and then turn towards the off position...this will allow you to dial temps down below the normal low setting. For smoke atg low temps, use chips...the smaller the chips the lower the heat required to make them smoke. In a pinch, you can lower the cast-iron smoke tray closer to the burner so it gets more heat to the smoke wood. For longer smokes, you can use a combination of very small to normal sized chips (faster onset of smoke, doesn't last very long), and add small and medium sized chunks (takes longer to start smoking and lasts longer).
You can use pea-gravel or play sand in the water pan as a thermal mass...line the water pan with foil after adding thermal mass...you can add smaller amounts of water to the foil liner, if you wish. Water will limit your high temp output due to the cooling effect of water vapor.
I fitted my Smoke Vault 24 with a 4" x 24" vent stack (light-weight metal pipe, just resting on top over the vent with a screened weather cap), and then I bent the tabs on the lower side intake dampers so I could fully close them...it doesn't seem to need them. This reduced grate temp variances by increasing the draft and may have had an effect on improving the smoke production due to not allowing as much fresh air into the smoke wood. Too much air and the smoke wood can flare-up and burn with higher chamber temps (high flame in colder weather, especially).
You will rarely find a smoker that works great in all conditions right out of the box...the Vault is among them. Once you use it for a variety of applications and get a feel for what you really want it to do, you can begin to understand what improvements can be made to enhance it's overall performance.
Be sure to level the unit very well before you fire it up or the door will leak like a sieve. Once leveled and running, you will find some leakage from the door, but it shouldn't have smoke rolling out of every nook and cranny of the cabinet door flange...if leveled and it has lots of leakage, the door can be tweeked for a better fit to the cabinet.
Flame should be blue on lower temp settings, and may have yellow tips on high flame...that's normal. They should not be completely yellow on high flame...if so, the gas mixture is too rich, caused by dirty burner or venturi inlet screen.
Shout back if anything else comes up, or I if I failed to answer all your questions. The SV-24 is a formidable rig. I've smoked a lot of good eats with mine over the years, then passed it on to my son who is learning the ropes with it. I'd still be using it myself if I hadn't decided to convert to the dark side (charcoal).