Tangs are relatively easy to keep. I have a Tomini, Hippo and a Purple Tang in a 75g and they all get along very well. My tank also does not have a speck of nuisance algae in it with those three in there. I do have to feed them nori daily, but I'm ok with that.
Keeping tangs.. Just be sure to have plenty of nori on hand for them as it makes up a large portion of their diet. Most are very active swimmers so a tank with lots of room as well as places to hide is essential. If you plan to keep more than one species, you will want to seriously consider adding them all at the same time to minimize territorial issues. As for pathogens, yes Tangs are more susceptible to Ich and other parasites, this is due to their having a much thinner slime coat than other species. Any risk of infecting your main tank can be avoided if you QT them in an observation tank for at least 2-3 weeks and be ready to treat with the appropriate medications, or utilize tank transfer methods and keep them out of the main display until they are completely free of the illness/parasite.
As for feeding I make up my own mix of food using raw oysters, silver sides, and various other meaty foods. I also prefer to use the Julian Sprung's Red Sea Weed by Two Little Fishes brand as it is whole leaf seaweed that has not been ground up. So it holds together much better and doesn't make a mess in the tank when my tangs go nuts over it.
Last thing to know is most Tangs do get rather large. So unless you have a 6' tank or at a minimum 75g with plenty of open swimming room, remember that you may end up having to pull the larger species of tangs out when they get 3/4 grown. Depending on the species this however can take a couple of years. A hippo will go from 1.5-2" to 3-4" in the first year then they tend to slow way down after that. The same goes for most other Tangs. So you can probably keep the larger varieties for a while before they need to be pulled out. Tomini's are some of the smallest varieties at 6-7" but are not as voracious eaters as say a Kole or Yellow tang, that get much larger.
Aggression in Tangs is well documented and some species are much more territorial than others. So research the species thoroughly before getting it, and remember that YMWV and the Tang you get may be a total butt-head and might have to be pulled out if they are very aggressive towards the other members in your reef.
In the end, tangs are enjoyable to watch as they are always on the move, and once they learn who you are will readily come up to the glass and beg for food.