Making a virtual pet game. How to make screen gui?

I was working on a virtual pet game, because i personally love virtual pet games, and i thought it would be cool to make one on roblox. A few problems i had, was i didn't know where to start. Heres a few questions i have:

1. How do you make the screen gui, where it shows your pet, and it shows it sitting with a room backround behind it?

2. How do you make screen buttons, where if you click, it feeds your pet (or something) and it shows a little animation on the screen gui where a bowl pops out, and the pet eats, and it also raises the pet hunger bar?

3. How do you make a hunger (and other needs bar) and make that if it goes down, the pet dies and you lose?

Also, the pet will be a baby dragon.

1. How do you make so there is a level bar, and if you play the game for a while, you level up, and the dragon/pet grows up?

2. how do you make minigames so you can play with your pet/dragon, for example, a flying minigame where you make your dragon fly and dodge rocks?

I would also appreciate if you just told me some good models, plugins, or guis good for this. (although i try not to use very many free models.)