Yes it is a good amount for investing for a long term investment. But if you are aiming for a long term investment with 1 bitcoin. I think that is not going to be enough because it is better if you are going to invest higher and going to add some amount to it. So that as you are waiting for a long time you can have higher income.
I think invest 1 bitcoin is quite enough, it's depend on the person though. But yeah, the profit will be small if you invest only 1 bitcoin, but the risk also not big, because you only invest 1 bitcoin.
If you invest 1 btc in altcoins then you can get higher profits and you can even double your 1 btc in quick time, its all about identifying potential coin before making an investment.