Sell everything never. Sell enough to have extra fiat currency for extra expenses like bills.
If 1 BTC goes to 40k selling 30%.
After the massive of bitcoins price, I'm not expecting anymore with the price increase. Because it will happen suddenly and that $40k will be a good price to sell but I don't want to make myself upset again. I want to see the price first to reach at $3k and that will be my mark to sell.
I dont plan to sell my bitcoins until they are worth 100k. I know it is a far fetched dream but I believe that once bitcoin adoption reaches global scale, it will lead to a financial revolution and reset. It will change the way people think about money. At that point, everything might be denominated in BTC instead of FIAT. I bought into btc because I believed in its concept, not because I think the price will go up.