How does the scoreboard work?

I started the money system on my minecraft server today. My friend and I considered how we want to call our currency. We decided to take toilet paper. Now I have some questions.

1. How can a player see how many toilet paper he still has in the scoreboard?

2. How can I make it possible for the player to withdraw money but not have numbers in the scoreboard (i.e. That he can't go further than 0)

3. How can I convert the toilet paper from the scoreboard to playerheads?

4. How can I make a player redeem a player head (which he has in his inventory) and then get money (toilet paper) in the scoreboard?

5. It would be good if you can do everything with buttons

Short question first: is this a plug-in or the / scoreboard command?

If possible with the / scoreboard command

Be sure to do that with plugins

So you would need a lot of commands for that. I've done it myself, but I can't find the functions. So as soon as I find it, I will write it in a comment on this answer, but in principle you create a scoreboard and then display the value with a screen overlay: https://minecraftjson.com/ here you can generate something like this. You do the rest with checking commands. To implement the buttons you also need a tellraw command here: https://minecraftjson.com/

I can't help you with / scoreboard. Better use a plugin - I find it much easier!

Which plugin would you recommend to me?

Hmm, probably more of an own one in that case. There are hardly any plug-ins that do this.