Lesson's or things I have learned about UDS's (personal opinions) in the last couple years:
1. Buying a clean new drum is worth it (unless you get lucky enough to get a cheap/free unlined drum w/ food safe oil in it). Also, if you can find someone to sandblast it inside out your avoid having to burn it out (some people will argue with I'm sure...). I spent $60 for a new drum and $20 to get it blasted. $80 is well worth avoiding hours of burning and sanding in my opinion...
2. Rustoleum flat black paint is your friend. Only paint the outside of your drum, the inside get "seasoned". Flat black is easy to touch up and actually blends in with itself. Yearly cleanup only take 5-10 minutes if you have a drill with a wire wheel and a can of this paint. I've just found w/ fun paint or patterns they end up looking like crap after a year or two and I'd rather spend my time cooking vs. stripping and repainting my entire drum.
3. Electronic controllers are wonderful. For day cooks I can get away w/ out them but for night cooks I'd rather sleep knowing everything will be ok. For example last week the temp outside dropped 30 degreees at night (wasn't aware it was supposed to) so I woke up to a brisket cooking about 20-30 degrees low....). I've had Wifi, digital display, and non digital display. They are all great but I've come to the conclusion a ique 110 and a wireless meat/pit thermometer do just fine. I'd rather spend less $ and keep it simple.
4. Season your drums inside properly and a rusty interior is only in your imagination. I buy 2-3 cans of canola oil from walmart and spray the entire inside. Light up some coals and let it burn at around 300 for a few hours and your done. Each cook if you notice bare metal spots spray a little oil before/during your cook and your good to go.
5. Weed burners are your friend. Lighting a drum becomes a 2-3 minute task. And until you learn to properly use it your neighbors might think jets are flying over head.
6. Read everything you can online and "borrow" ideas from everywhere and everyone so you end up creating your perfect drum. It will take building (or rebuilding) maybe 2-5 drums before you find what really works for you unless your lucky.