All answers here are obtained from http://forum.xda-developers.com/showthread.php?t=2010338 in order to benefit the community here. Credit goes to the original author. Head on to the link to read the full version as those that are listed here are only the important/main points. Some additional points which are not available on the original thread are added, tho.

What is “root”?
Root essentially means that you have root (or superuser) access to the file system on Android. It is similar to being “administrator” on a Windows PC. It has nothing to do with your device or the bootloader, it has to do with the Android OS (i.e., you cannot “root” your device – you root the Andoid build that you are running). To have root, you need to be booted into the Android OS that you have rooted. If you are in fastboot mode, root is irrelevant.

What is a "bootloader"?
Without getting into too many technicalities, the bootloader is essentially the program that gets loaded first when starting your device, and it is responsible for booting the Android kernel. Think of the bootloader as the BIOS of a computer.

What does it mean if my bootloader is locked/unlocked?
Most (if not all) devices are shipped from the manufacturer with locked bootloaders. This is for security reasons. A locked bootloader does not allow easy flashing of images, which means that it is difficult to change or modify the operating system. Unlocking a bootloader (using fastboot) on most Nexus devices results in a complete loss of all personal data from the device. Having a locked or unlocked bootloader has no bearing on the functioning of the device. Unlocking it gives you more options to play around with the OS. Additionally, an unlocked bootloader means that you can easily root your device no matter what -- unlike most non-Nexus devices, if you lose root, it is trivial to get it back.

What is "recovery"?
Recovery is like a mini OS, which allows you to perform various functions, usually related to flashing files to your device, or updating files, or backing things up, etc. The stock image has a recovery included, but its functionality is very limited. There are a number of custom recoveries available, but the two most popular for the Nexus 4 are CWM and TWRP. There are various versions of each. More details to come in this section.

What is a "ROM"?
A ROM is slang for an mobile OS build.

What is the difference between a "stock ROM" and a "custom ROM"?
A stock ROM is a ROM that is built by Google and is signed by Google’s platform keys. Everything else is a custom ROM.

If I unlock my bootloader, is that the same as root?
No, as was mentioned above, unlocking the bootloader allows you to (among a few other things) flash images easily to the device when not booted into the Android OS. Root allows you access to manipulate the files WITHIN the Android OS.

If I want to root, do I have to unlock my bootloader?
Yes. Because you will have to flash custom recovery in order to flash a file which grants you root access. For more information on rooting, refer to following points in spoilers within this post.

If I unlock my bootloader, does that mean that I have to root?
No.

If I unlock my bootloader, do I have to flash a custom ROM?
No.

Do I need to root to flash a ROM?
No.

Again, these FAQs are not written by me and is obtained from http://forum.xda-developers.com/showthread.php?t=2010338. Credit goes to the original author. Click on the link to read full version of the basic information as those listed here are summary of main points / important points only.

Wug's Nexus Root Toolkit
http://forum.xda-developers.com/showthread.php?t=2015469
Video tutorial:


OR..

mskip's Nexus 4 Toolkit
http://forum.xda-developers.com/showthread.php?t=1995688

Prerequisites before unlocking & rooting: The Drivers Installation
1. Download Universal Naked Driver
2. Uninstall any current existing drivers for your Android Devices (Right click Computer > Properties > Device Manager; or just use the RUN COMMAND (Windows Key + R) and type 'devmgmt.msc. Reboot your PC after uninstalling these previous drivers.
3. Plug-in your android device to your computer, and then follow the instructions listed by Google; except replace the driver selection with the Universal Naked Driver you previously downloaded.
4. After you have successfully installing the drivers, proceed to the link below for Android SDK installation (for fastboot & adb) and finally the unlocking process; custom recovery flashing & rooting.

For full guide, refer to this link: http://forum.xda-developers.com/showthread.php?t=2018179

Ensure that you install Universal Naked Drivers instead of the default LG / Nexus drivers.

Head over to the link above to download the drivers, and then use google's instructions to install the driver and browse for the folder extracted from the .zip file you downloaded (instead of Google's driver).

Head over to Nexus 4 @ XDA-Developers and have glimpse at all the available custom ROMs, kernels, customisations, themes, applications and etc.

Head over to this link to read on what steps are required to revert to stock:

http://forum.xda-developers.com/showthread.php?t=2010312

In order to check your CPU bins, you must be rooted and have Android Terminal Emulator installed, then follow the steps below:
1. Launch the 'Terminal Emulator' application.
2. Type 'su' and hit Enter.
3. If there are any pop-up prompts requesting for SuperUser access, GRANT it.
3. Type 'dmesg | grep PVS' and hit Enter.
4. It should return a line and show you whether if yours are SLOW, NOMINAL, FAST or FASTER. If it does not return these values, try rebooting your device and try again.

Note: This might not work on custom kernels as kernel developers might have changed the return value.
Credits to XDA Community for the original thread.

- SGP Stenheil Ultra Oleophobic/Crystal/Crystal DUAL (Dry application) > Only Crystal DUAL includes front & back


- Nilkin Crystal/Matte (Dry application) > Comes with front-back and front only pack (confirm with seller)


- Best Skins Ever Total Body Skin/Total Body Skin with Case Optimized Screen Skin/Screen Skin/Case Optimized Screen Skin/Body Skin (Wet application)

*These are all gathered through search from Bulk Orders and Garage Sales. I might not have included all of them but you can always do a search for "Nexus 4" for more accessories selling threads. Feel free to PM me your thread link if you are selling accessories for Nexus 4.

Disclaimer: Do note that by no means the thread starter is associated with any of the seller below. The link is collected and put up in order to provide conveniences to users in this thread. At any given time that warning of taking down the links are given; they will be removed without any objections.

Garage Sales:
lemonzaiii - http://forum.lowyat.net/topic/2675132
sakurazz - http://forum.lowyat.net/index.php?showtopic=2671048
tskhor - http://forum.lowyat.net/index.php?showtopic=2629022
ping325 - http://forum.lowyat.net/index.php?showtopic=2455125
cougar richard - http://forum.lowyat.net/index.php?showtopic=2664356
pu27 - http://forum.lowyat.net/topic/2682523

Bulk Orders:
Doomsday - http://forum.lowyat.net/index.php?showtopic=2634006
Racerx - http://forum.lowyat.net/index.php?showtopic=2660339
Dark Devon - http://forum.lowyat.net/index.php?showtopic=2672546
Shirogawa - http://forum.lowyat.net/topic/2407663
cjlai - http://forum.lowyat.net/topic/2696828/

Head over to MyColorScreen to have a glimpse at other's work to have inspirations; or directly use their customisations (if they provides tutorial or files required). Alternatively, view the previous post Homescreen Gallery to look at other member's customisation work