I would amp the rear speaker to the sub.
Components are vastly better, the more you spend the better you can get, but can still get some decent stuff for little over £100.
Mount anyhow you can, a lot cut MDF templates to use between the door and speaker, in an ideal world the tweeters will be as close to the ear as possible, but failing that certainly angled towards the driver/passenger.
The BOOM comes from the rear, the quality comes from the front.
The current JBL GTO 628 in Halfrauds is a good deal, very nice clarity.
Connection is quite easy, don't waste your money on so called "special" wire for the LIVE amp feeds, just boggo std wire of suffecient rating will be fine, ALWAYS fuse the wire as close to the battery as you can, any run that goes through the car.
Also take you earth direct from the battery, it is a lot lees prone to picking up noise this way.
Keep the power leads down one side of the car and the RCA leads from the headunit to amp/s down the other side, put next to each other can generate noise, usually heard as a fuzzing sound.
I would use gold plated connectors on the amp terminals, this is not to "speed up sound" as I've heard some muppet say, it's merely the best corrosion resistor know to man, and the boot will get a surprising amount of moisture in it.
Don't set the amp gains too high, set volume on say 1/3 on head unit and adjust amp gains so that it is a nice tollerable sound, turn the gains up too much and damage could be caused.
Take your time and don't bodge, like most youngsters, possibly cause they're strapped for cash!
The set up I took out a civic a few years ago blew the fuses with the previous owner, so he replaced these with 3/8" solid bar!!, and the moron had two fuses for each amp right at the amp themselves, so nothing to protect the actual wiring itself.
tabetha