This app was mentioned in 3 comments, with an average of 1.33 upvotes
There is actually one that already exists, looks great and also have a colourblind mod :
Android : https://play.google.com/store/apps/details?id=com.aurelhubert.truecolor&hl=en
iOS : https://itunes.apple.com/us/app/true-color-stay-focused-on/id995939395?mt=8
1) Launchers replace the system UX with its own specialized UI. It's all personal preference. Some people like me love launchers, some others believe it ruins the "LG/Samsung/HTC/Sony experience". It's all up to you bud
2) As I stated earlier, it's up to you. I prefer certain launchers because I like taking full advantage of the phone and it's OS. I recommend Nova Launcher. Countless theme packs and what not. It costs 5 bucks, but it's worth it IMO. As with the stock UX, you can only customize it in so many ways. Take your pick. Even if you choose to go with the plain stock UX, it's one of the best skins. Way better looking than Shit-Wiz
3) Greenify is love, Greenify is life. If you're not a heavy music streamer, and just like to have all the music downloaded on your phone, use either Poweramp, or Shuttle as your music player. Evernote is great if you like keeping lists, schedules, and what not in one place. Also, IMO, the stock messaging app is garbage, so I use Textra. Nice clean looking app.
4) Not a huge mobile gamer. I only really play DoodleJump, Case Clicker and Quiz-Up. If you like brain games, then "True Color is a good one. As for MMO type stuff, I don't really know about those. Never been a fan of the genre.
5) The Camera is pure sex. It's one of the best smartphone cameras out there, so you might suddenly become obsessed with taking pictures of stuff like I did. As for accessories, dbrand skins are pretty slick. They keep the thinness and curvature of the phone whilst protecting it, unlike cases that opt for durability rather than thinness. I personally love the carbon fiber and wood skins.
Enjoy your new G4! Have fun OP! It's your phone, make it however you want!
Edit:TIL I suck ass at formatting.
Reminds me of True Color https://play.google.com/store/apps/details?id=com.aurelhubert.truecolor