Remember that to have a line array you have to have it coupled with the ceiling and floor.This means that you need to have the array big enough to have the mid ranges at least be a length that is 70% as long as the height of your room. Otherwise you have a line source but not a line array. You won't be in the near field for listening, and you will have all kinds of problems with the sound of the system.
Crossover will be critical to determine the maximum center to center distances for the midranges, and thus the amount that you have to use.
You can get an analog Rane Ac-23 two channel three way crossover on ebay for about $115 - if you wait and work for a good offer.
Marlboro