For the center speaker, which I assume has one output from the amp, and two inputs to the speaker. The simple thing to do is run the + from the amp to one of the + on the speaker, run the - from the amp to the - on the other terminal, then run a single wire between the + of of the one terminal to the - of the other terminal. That is series wiring which will make the amp see it as a single speaker with an 8 ohm load. Much like this:
As for the full range boxes, wiring isn't generally as tricky as you think. Tweeters typically don't throw the ohm load off much. I would highly recommend getting a $20 multimeter from anywhere (I got mine from an auto parts store) and check the ohm loads while building the setup.
Here is an article on wiring and ohm loads:
For crossovers, I would only really worry about it on your stuff like midranges and tweeters. A simple passive crossover consisting of a single capacitor each will probably be sufficient.
Check this link:http://www.bcae1.com/passxovr.htm
I would get into it more with you, but I have to get ready to go to the Richmond Indy race today.