An active crossover is an excellent idea for a line array. You'll have to account for the extra amplifiers you'll need and cabling as you realize. The benefit is that you can optimize each band some better and get better results than from a passive crossover. You'll save much time and hair with an active crossover. You will likely need a measurement system to get decent results.

Each active crossover--Behringer, Ashly, BSS, DBX, Rane, etc.--have advantages and disadvantages so it is worth reviewing just which crossover would work best for you. Read some or message boards and hear about just how much efforts the users need to get good results. For what it is worth, I'm using a DEQX crossover and it is very slick but not cheap.

Let us hear how you progress.

Jim