How to make a cash leaderstat, getting more cash from killing, and use it in a gui shop?

I'm trying to make a game but I'm not "the best" with scripting. In my game every player getting a laser gun(hyper gun(ID:131222609)) and the thing that I want to script is this:

1. When do you shooting a player, you will get 15 cash(I want to name it Pixels, and there will be a a leaderstat of this on leaderboard) and the player you killed will lose 10 cash(Pixels). There will be a Gui Shop on screen(enter shop button: position:{0, 0},{0, 250}; Size:{0, 150},{0, 50}; Style: RobloxRoundDefaultButton; Font: Arcade; Text: Shop; Text Color: 255, 255, 255; Text Scaled = true) and you can click it to open the shop and use the Pixels to buy new things. I will often add new things to buy in the shop. can you do a simple way to add new things to offer in the shop? (every itemOfferButton in the shop need to had a picture of the item :3 ) Note: I need to use the same leaderstat of cash in all of this things, so make sure it's using the same IntValue.

2. I also need a levelbar on leaderboard. You will level up when you will kill some people. Higher level will make you more faster, stronger and will give you new abilities (that i will add) I want to write how many players you need to kill each level to level up so please make it easy to add levels/change them.

Please help me :3

barkinght123