So yea, why not I share customization tips.
even since RAZR, I've been customizing my UI with a lot of stuffs.
But with Z Ultra, I did extra stuffs just to keep me happy.

1. Nova Launcher Prime
- yes the stock homescreen is good but it doesn't do gestures. I use Nova for its stability, customizability, and usability. Never again my finger had to crawl way above the screen to pull the notification bar or to aim the app tray icon to list all my apps.
RAM used: ~55MB

2. ROM Toolbox Pro
- It's not just to manage the custom recoveries or playing with kernel. For basic, I use it for changing my font and boot animations on-the-go. it's also the swiss-army-knife for rooted phone.
RAM used: none for font/boot animation tweaking.

3. roundR
- I don't really mind having rounded corner screen on my true black screen panel of XZU. the effect came out nice.
RAM used: ~16MB

4. GMD Auto Hide Soft Keys
- 6.44" is large but it's not 100% usable due to XZU having the soft navigation menu. Use this and tada, gone!
RAM used: N.A

5. Button Savior Pro
- Now that you removed the soft navigation, u can use either GMD Hide Soft Key's very own soft navigation or u can use this Button Savior. Button Savior Pro have much customization and better trigger positioning.
RAM used: N.A

6. Gravity Screen Pro
- thanks to uncle @benny888, this app is really good for me although I use it juz so my screen turned itself off inside my pocket. may seem like simple stuff but when u get used to it, it's really making ur phone somewhat smarter with its surrounding.
RAM used: ~2.7MB

7. SlideIT Keyboard
- Resize, cursor navigation, skinning, all I ever need for a keyboard. very good language, swiping and dictionary support too.
RAM used: ~17MB

8. Slider Widget - Volumes
- My homescreen quick volume access widget. Also adjusts my brightness settings.
RAM used: N.A

9. SoundAbout Pro
- As an avid mobile multimedia user, I always carry around a portable bluetooth speaker with me. However, not ALL sounds go to that speaker (such as alarm tones). With XZU's internal speaker, I will never wake up so this app helps to divert ALL sounds to my bluetooth speaker whenever connected.
RAM used: ~2.7MB

hope u peeps find this useful