To be safe, get two Bitcoins.
lol i agree with this. in 20 years 2 bitcoin may be worth 2,000,000$ and to me a 2m retirement fund would last if you plan on retiring at 60 and living untill 75 or whatever. specially if you have another income coming in still from ssi or whatever it may be
safe side get 5
That is not easy. Just imagine if in the first year of your retirement the Bitcoin price will be $700. If you have 5 BTC that same as $3500. I guess you will spend this $3500 in the first year. The next year you will do not have anything.