There is a multitude of free information out there on what to buy, how to build, test and maintain your new rig. Here is a short list that I will be updating with suggestions.
PC Part Picker
Logical Increments AKA Falcon's Guide
144z Monitors' Guide
Graphics Card Hierarchy from Tom's Hardware
CPU Hierarchy from Tom's Hardware
Choose My PC
Newegg Video Guides
LinusTechTips Holiday Budget Rig
NZXT Build Guide
A 5 year old builds a computer with her Dad
Ninite - Grab useful software all at once.
Prime95 CPU Stress Tester
CPU-Z Monitoring Tool
NCIX Tech Tips Guide for Hardware Monitoring
Unigine "Valley" Benchmark Test
I'm at a loss to populate this section. Will happily add some suggestions.
How to Clean your Computer from Newegg
This is a nice list! I think a Power Supply Calculator might be helpful as well in the buy section.
As for physically maintaining a PC, keeping it clean of dust/hair/crud is important for maintaining airflow, and really all you need for that is a can of air and a shop-vac (Or if you're paranoid, an anti-static vacuum).
When it comes to maintaining the OS, that's a bit more in depth, but just basic things, like keeping your OS patched, along with any third party software. (I'm looking at you Java and Flash) Keeping your drivers up to date.
This might also be the place to add in a suggestion to use Ninite to grab software when the build is complete.