distribution blocks are for splitting 1 big wire into numerous small wires.
http://www.sonicelectronix.com/cat%5Fi205%5Fpower-distribution-blocks.htmlas far as cost they are pretty much the same. the reason for using a distribution block is basically for people with a few amps but for just 2 amps its optional.
the reason full kits are a waste is because they are designed to reach to the trunk space area. 4 channel amps generally get mounted under the front seats so you have like 10 feet of extra power wire.
also since i did forget something you will need to buy a roll of speaker wire as well for wiring the new speakers to the new amp.
http://www.knukonceptz.com/productMaster.cfm?category=TCA%20Speaker%20Wire you'll need like 50 feet of the 10 gauge.
ya i was afraid of that backorder thing. there was 1 left when i linked it. so ya just order that one its the same.
i'm not really sure what you mean by the general guideline thing? like a step by step of what to do or what?
the amp installation is pretty straight forward except for the 4 channel amplifier will require you running new wires to all 4 of the door speakers.