You should never sell bitcoin and always think to accumulate them. The future is of bitcoins and i believe that those who do not have bitcoin will be left behind.
You can trade or sell your altcoins but always keep on holding bitcoins.
What is your target price for Bitcoin, i bet you wont be holding the coins for decades, but there should be a target for you and i would like to hear that valuation.Bitcoin is all about making transaction and that is what it is intended by Satoshi and not to hoard them, if so it will defeat the purpose of the creation.
When we talk about the risk factor, it all depends upon the entry, you cannot enter when the coin is rallying and expect to make a huge profit in a short period of time.