[General Topics] EZ-Poop:
This tutorial will show you how to setup your device as admin and configure other user profiles (this is important when you're not the owner). Your device maker disabled multiuser functionality in Kitkat, like on my Lenovo Tab 2 A10-70L? - then this for you. At least, that's where this procedure is tested on. Afaik, this should work on Lollipop too. But will it work for your device? - No clue, you tell us!

Basically it's an accumulation of what I've read here (thanks again) and my personal experience as a noob myself. ;)

So far, this guide is incomplete and I'm hoping for some pro tipps to perfect it. Please help me sort out the unclear parts highlighted in red and I'll update this post accordingly. The sooner the better, because this actually is not my device and someday soon I'll have to pass it over to my mom since it's my present to her, I'm only setting this slab up... ;)

Preconditions:

Android treats the first account created as "owner". Only owner will have root privileges if installed accordingly (=admin).

Root permission and a file manager (e.g. ES File Explorer) are required for this fix so go get that first. For the Lenovo Tab 2 A10-70L, I followed this beautiful guide, besides that, I can't help much here.

Unable/uninstall all bloatware (I was adventurous with Titanium Backup with no probs so far, but some crap remained from looking at new user folders; still in search of a vendor/device-specific "save to remove" list)

Install ALL apps you and the other users suppesdly need. This will avoid the need to redownload and reinstall all the apps for each and every user wasting storage. Think thrice, usually it'll be more than desired, but better you do it instead of a DAU... ;)

Each user will be able to install apps later though. Full control over user restrictions can be applied for "guest profile" only.

Steps:

In file explorer, go to /system/ and open build.prop

Check if you have anything like the below text (you shouldn't, otherwise edit accordingly) and add these lines at the end of it:

# Multi Users
fw.max_users=[COLOR="DarkGreen"]X[/COLOR]
fw.show_multiuserui=1

Replace X with your desired digit (up to 7?)

(I've read somewhere that 7 users is maximum that system can handle, but I haven't tried)

Save, reboot and log in as "owner" (your profile)

Go to Settings>Device and say hello to new item "Users"

Create new users and/or a guest profile (important: write down the order in which you created them!)

All new user profiles are now shown as "new user" no matter what you wrote in the profile properties (only guest will be shown as "guest"). Mind you, this also applies for the lockscreen!

In file explorer, go to /data/system/users/ to find your users' folders containing some system files (what exactly?) Now guess what - the order of the numbered folders and #.xml files match the order you created them. "0" is you, the owner.

Open each .xml file and replace "Owner" with "Your Name" and "New user" with "Username"

Put the device to sleep, trigger lockscreen and log in to each user profile and

Pull down shortcut menu from top right and enable autorotate

Go to Settings>Users>Security, check all settings and note each unlock-code

Disable background services like sync, location, etc. that could potentionally drain battery where applicable

Rinse & repeat 8) for all new profiles

Install "Multi-User App Share" and set apps per user. (Or is there a newer app or more hackish approach without the need for xposed or compiling stuff etc.?)

= DONE =

If you want the user icon in status bar, follow http://xdaforums.com/galaxy-note-3/themes-apps/multi-users-mod-t3017782/post58659868#post58659868 (haven't tried that ).