T lines do need to be properly designed and for the most part aren't used as subs as there are better/smaller ways. Full range T lines that will go to 20 Hz are viable- see Legacy.A baffle board only works but you give up a lot of sensitivity and bass response with them. Some people like them a lot- try the planar forum at Audio Asylum.
Bi-amping requires an active crossover to operate.
Arrays can be built 3 way or 4 way if you wish, but most are 2 way.
I don't understand the last question, but I do use both EQ and a limiter on my HT system.