Paypal integration question

Hello guys, i have few questions about paypal integration, it's the first time i have to do a paypal integration. (i'm doing it on a php panel i bought)

1) What is the difference between : Live environnement and Sandbox (test) environnement ?

2) Is uploading his Paypal Client Secret & Paypal Client ID is risky ? Can someone withdraw my money balance with it ? what the risk if there any risk ?

Question 3) & 4) are not really web-design related but i think someone who can reply to 1) & 2) should know about it.

3) my account is created since 2009, i never had any trouble with transaction on paypal and i received for more than 100k $ of paypal "gift".

I would like to accept "regular" paypal payment but i'm affraid to get scam. Is having a 11 years account with 0 disputes will drastically help me to no being scam by customers disputes payments ? Or paypal will solve the dispute like any others accounts.

4) If i decide to use something like coinpayment to cashout every transaction from paypal to bitcoins (so i dont get scam by a customer dispute) and paypal ask me to refund him when i have 0 $ in my balance. What happens ? They ban/freeze the account until you can refund ?

Thanks guys, i love you

i can only answer the 2.

put all cour credential in the variable environnement, and some server has the options to hide the credentials.

here an example

https://devcenter.heroku.com/articles/config-vars