It’s all fun and games until the taxman passes. There is no clear legislation on taxes and it varies on per case and per country basis. My personal recommendation is to declare the money you cash out on your tax form. This would normally be taxed as « financial income money », just like if you sold shares or cashed out money from the income of your own company (like when you get paid dividends). Example: 15% financial income tax. You cash out 10000 EUR, you get taxed 15% on this.
Arbitraging can be very lucrative especially with Asian markets (South Korea for example) where cryptocurrencies are exchanged at premium rates, but due to the high volatility of the markets and the congestion on major cryptocurrencies (Bitcoin and Ethereum) it is becoming increasingly difficult to do arbitraging because of potential incurred losses. Add to this the fact that exchanges need a certain amount of confirmations before balances are made available for trading and it makes it quite risky at least for Bitcoin and Ethereum.
The list of stock brokerage firms is updated throughout the year. TradeMonster, MB Trading and Scottrade were removed from the table above, since they got acquired and merged into Etrade, Ally Invest and TD Ameritrade respectively. In addition to keeping stock brokerage companies list current we also update broker's rating and pricing, which are often correlated. 

As written in section Investing 3, you should never keep any valuable assets on an exchange, unless you engage in day trading. You should get an appropriate wallet to store your cryptocurrency safely. To explain the concept better, what you are storing is not the cryptocurrency itself, but your private keys, the keys that allow you to spend the cryptocurrency that is assigned to you and stored on the blockchain of the given cryptocurrency (of course each project has its own blockchain, just like each bank has its own internal banking system – to simplify heavily). Anyone who has access to your private key is in control of your cryptocurrency assets, so you must secure them. Most if not all of the wallets around have a feature called a backup phrase. It is a mnemonic sequence of words that must be written on paper and stored securely. If you lose access to your wallet, get it lost or stolen or whatever, this backup phrase should allow you to recover instantly access to your private keys and funds, after which you should immediately transfer them to a new address.
You’ll come across an overwhelming amount of information as you screen potential business partners. But it’s easier to home in on the right stuff when wearing a “business buyer” hat. You want to know how this company operates, its place in the overall industry, its competitors, its long-term prospects and whether it brings something new to the portfolio of businesses you already own.