The legs on the ash can really aren't necessary unless your intakes are to high. Rule of "UDS" thumb is your intakes should be lower than the basket. Most have 2" legs on the baskets with intakes at about 1-1/2" from the bottom of the drum. As long as you fall into that category, no legs on the ash pan required. That's what's neat about UDS's though. You can build them the way you want. As long as it can maintain whatever temp you like cooking at and turn out great tasting food, that's all that matters.
As far as the use of a diffuser, water pan, or nothing, that's personal preference. Some use them, some don't. That's one of those Chevy vs. Ford vs. Toyota conversations. Are they required? Depends on who you ask.
Some folks like the water pan cause they say it adds moisture, some say it doesn't add moisture but helps maintain a constant temp, some say it doesn't do anything.
Some like diffusers because they help add a turbulence to the heat rising off the basket and helps to get a more even temp throughout the drum. Some will drill holes, some don't. Holes will allow fat and juices to drip on the coals and add more flavor. Diffusers without holes, just catch the juices and fat and let them boil away.
No diffuser or water pan allows a more direct heat to the bottom of the meat and allows all the juices and fat drippings to get to the coals. Some will say that this helps with faster cooks and creating bark on the meat. Also that it adds more flavor.
My point is, everyone is different. It all depends on what works for you. I personally use an old ECB food grate covered with alluminum foil as a diffuser on short, 6 hr or less cooks. No holes. I usually set it about 1-2" above the basket. For longer smokes, I'll use a water pan. It's what I have been successful with so that's how I UDS. My top rack is approx 18" from the top of my basket. This is about 1" down from the top of the drum casue I'm using a dome lid. My basket is 12" deep and about 14" dia. It can hold 30+ lbs of Stubbs Hardwood Briquettes and whatever wood chunks or chips I choose. Longest I have gone is 16 hrs and still have half a basket of coals left.
Hope this helps.
Chad
