So, for 50 btc, I will give it a go.
If i where you i would try to go on a big market where you can actually spend that much money.
I do not believe you can cashout 8000 btc in one day, this process will take month. This is not so much because it is hard to cashout, but because you went from "normal guy" to "extremely rich" and you do not know how to navigate in those water. You have to learn and to find helpful people which needs trust, which needs time.
Your main problem is to have a bank account and an exchange account in a country where the marketcap is very high.
If you go through a broker you will still need to get a bank account in a country that is not yours.
My solution is the following :
You have so much money you can buy yourself a new citizenship. This is also a gift for your childrens as they will have 2 different citizenship giving them much more flexibility in the future.
I would choose either Malta or Switzerland.
MaltaMalta gives you EU citizenship which in turn gives you the possibility to live anywhere in EU. On the downside, you will have to pay the 30% flattax on your capital gain. Go and check this page for information
To get citizenship, you have to :
-> pay 650 000$ to the government
-> Buy 350 000$ worth of real estate ( and keep it 5 years)
-> Buy 150 000$ worth of malteese investment
check here for more details
http://www.maltaimmigration.com/Which mean, you have to first cashout at least 1 150 000 $. I belive you can do it in your country.
Note that after this process that can be done in 3 month, you will already to sell bitcoin for € and transfer it to yourself.
Then they will give you a eResidence and you then have to live 1 year in Malta, After a year, you will be Citizen of Malta and the EU. You can easily extend this citizenship to your wife and kids.
Citizenship canot be removed from you, which mean this all process is a lifetime bonus for you and your kid.
Cashing out in Malta might force you to pay the 30% flat tax. Depending when you do it, you might still be fiscaly in malaysia and thus pay 0% tax. But you have to (triple) check this out.
SwitzerlandSwitzerland is not so straightforward to get as Malta, BUT the taxes are much lower (1% or less).
I am much less aware of how to achieve the same thing but i am sure it is possible. Switzerland is a federal country, which means it should be considered as various little country, and the process/ tax might depend on the "canton" you actually choose to live. Genève or Zurich will probably be the best choice.
The process to actually get citizenship will need you to live in switzerland much longer (6month+/year for 12 years) . But you will get permanent visa fast and be able to cashout easily.
I would choose Malta if you do not care of paying 25 000 000 in tax but want to go back quickly in Malaysia. Otherwise i would choose Switzerland.
Regarding forkcoinDo not forget to cashout your altcoins! Bch/bcg/btx/... /bcd( last !)
Other optionYou can alternatively create a company in a big marketcap country ( never forget taxmen) and sell your bitcoins to a bank account belonging to this company. That would secure your exit price. But then will come the question of how to legally use this money that now belongs to your company...