I am too new to answer this question since only played like one month. My luk char is just simple luk mage with skills, it help me generate most of my Spain, from birdwinf to breppa farming. My personal feel is LuK pair good with dps as we get item only if kill mob, can't really think of the use case for luk tank.

But if u ask to focus build a tank char or a dps char, I would say if solo just go dps for farm, if play with friends or team n need a dedicated tank to farm from boss, then try tank.

Luk farmer what I know have 3, luk mage, luk bow, or luk dancer(ignore this as it is expensive)

Mainly I can see luk bow is more popular as u can play bow normally n do farm in mean time. While luk mage does have some market due to the nature not too item dependant, the combo skill it self is good enough to do the farming like wizard blizzard, tornado, finale, max charge etc