Have a look at ESP. (http://sound.westhost.com ) Apart from being an informative read in general, his kits are highly regarded and he has numerous articles relevant to your situation.
What I suggest is using chip amps with line level crossovers where possible(2nd order passive line level high pass http://www.t-linespeakers.org/tech/filters/passiveHLxo.html and 4th order active lowpass) Using small drivers FR with a 2nd order butterworth highpass network at the –3db point (sealed box with Qtc of 0.707 (Butterworth alignment) of the FR will give you 4th order Linkwitz Riley alignment. The lowpass can then be constructed either with a simple opamp buffer to sum the two channels followed by a 4th order Linkwitz Riley highpass section as per ESP. This should give you an acoustical 4th order crossover with minimal investment in components for the electronics.