Stop buying bitcoins when you have a lot of money already invested in it. Bitcoin is unstable so this means that it can go down so you can lose all of your money.
Never do all in because that is not logical.
That's a good idea. If you already have enough, then stop buying bitcoin. But if you think your bitcoin in your wallet is not enough, then continue buying if you can still afford the price of it. AS long as you can still afford, you can actually buy anytime. The only problem if we don't have enough money to buy bitcoin, that's the time that we also need to stop for a while.