So I bought BTC at £9000, made a nice amount. Is it a good idea to now sell this and move that money into alt coins? or should I sell half BTC and buy back in after alt season is finished?
What do you think?
You are asking us? All answers you will get will be to keep holding. What was your plan when you bought? Since you obviously entered Bitcoin to make profit if you are asking when to sell. Without having a clear plan and targets set then you can consider yourself lucky to have made this kind of profit.
My plan was to hold, which I did, I may take some profit and use that for Alt season. I don't know about lucky - if you buy and hold then sell at the right time you make money.
Holding a large percentage in bitcoin will help you when things go wrong. If you take all your profit and put it in altcoins you should know the risks involved. I am investing in altcoins but in a way that this won't be harmful to my total investment in cryptocurrencies. Any altcoin investment can easily go down 90%. Bitcoin when it reaches the top it can go down 80% but probably no more, unless it becomes completely useless. What I would do in your position is to take half out in cash. As I understand this, you entered to make more money, as everyone else. If you believe that cryptocurrencies will have a future, then you should hold your initial investment in it for longer. However, since the profit you've made is 4000% taking some back will mean you were successful with this trade.
By saying you got lucky, I meant that you entered the right time but not having a plan usually means trouble. You had the ability to see an opportunity that was there, but this is just half of it. The rest is making a plan and sticking to it.