The best advise that I could give you is to browse through the forums and find an existing design that you could copy. The thing that makes this stuff so hard, especially for us amatures, is designing a crossover. If you go with an existing design, then you can also copy the crossover. If these speakers are going to be mainly used for hometheater, then I highly recommend the Seos-12 or 4pi designs as they are very highly regarded and already have the designs published for you to read and copy. From what I have been told, either one of these speakers will be comparable to commerical speakers that sell for between $3,500 and $4,500 for the set. I am actually going to build some of them myself.
There are other ways to do the crossover, you could always do an active crossover, (active crossovers involve having a signal device such as the Behringer DCX-24/96 to split the frequencys up and apply the proper filters to the drivers, and each driver will require its own amp channel, so that means if you build a trio of speakers for your left/center/right and each speaker having 2 drivers each, you would need 6 amp channels as there are 6 drivers.