#1) You need to get the A/C system for your specific car. Different trim levels of the Civic will have different hardware because of engine and dash differences.
#2) This is NOT a do-it-yourself job if you're not familiar with cars. It's extremely labour intensive, will require running wiring all over the place and may even require punching holes in the firewall.
#3) This will be expensive. The "complete system" on E-bay (aside from not being for the same car) doesn't even have the wiring to hook this into the car's system. You'd need a new wiring harnes and the new climate control panel for the A/C also. I would not be at all surprised to see the total cost run upwards of $1,000 at a reputable shop.
#4) An OE A/C system is pretty much the only option. While there are generic kits out there, the do not work nearly as well and they tend to be of low quality.
ZV