10 to 50 btc is enough to retire for your future or to start a business to your own.. so that your family will be live well in the future..
more if you can gather is better you never now what price will be
but if price is good 10 may be more then enough
Yeah it will totally depend on the price of bitcoins as if price goes higher then even 10 btc is more then enough to take care and if not then even 100 btc would not be sufficient.