What do you think about Ethereum? Is it a stable crypto? 

Using any cryptocurrency is a risk, and you should understand this if you plan to work with cryptocurrency. The type of cryptocurrency you are talking about is relatively young. But in principle, I think this currency is quite stable so far. By the way, you can read this https://perfectial.com/blog/ethereum-switches-to-proof-of-stake/ . It is about ethereum blockchain, and I think it can be useful and interesting for you