Bitcoin has a refuge value side. But since we are not immune to big trend in the financial world, it may not be a bad idea to hold a little. For the gold, it is said that we must not exceed 5% of our portfolio. For Bitcoin, I would say that we should not go over 1%
That depends on your risk-taking capability. If you have no mortgage going, and if you are optimistic about the future of Bitcoin, then there is no issues in Bitcoin occupying as much as 20% of your portfolio. And there is no such limit for gold. It is a very low-risk asset. If you want, you can fill 100% of your portfolio with gold bullion coins and bars.