If you have 70 BTC I would not state that publicly if I were you. Just to provide you the information, there are a lot of warnings about publicly stating personal holdings for a variety of reasons, primarily because of hacking precautions.

But to answer your question, if you are holding that many BTC it can be an idea to diversify. Sell xx percentage as a risk-management decision, and keep the rest. It also depends on you buy-price, but since you are holding that many, I assume you got in in the early days.

Personally, I would sell 20-30% and keep the rest long term. Or maybe allocate 15% to altcoins and sell 15% into fiat. All depends on your risk-aversion and your buy price.