I understand that 'BIG' means different to different individuals. Here by 'BIG' I mean life-changing money (bigger than 20x of your monthly income).
For me, 20x my monthly salary would not change my life. It's a good amount, but it's not that much.
1. Let the money sit in your bank account (wallet) for at least one month. It will allow you to settle down your heightened emotions. Just let the amount sit and do not do anything with it for at least one month.
They say the same thing about an inheritance but for six months. Anyway, I don't think you have to be too strict with this, you can go to good restaurants at the weekend while you think about what to do. The point is not to spend it all in a hurry.
2. Go on a low-cost, week-long vacation with your family and friends (do not tell anybody about your winnings; do not boast) immediately. It will help you make your relationships stronger and will certainly help in doing step 1.
Not bad.
3. Do not change your lifestyle immediately, as it will help you to remain disciplined, which will eventually help you out to earn even more.
I agree but with a 20x my monthly salary I don't need to make an effort not to change my lifestyle
4. Consult a certified financial consultant and invest in a diversified portfolio other than gambling, probably for the long term, at least 80% of your winnings.
I'd do sth like that but I don't need a consultant.