Don't sell any Cin, just buy on dips until 10k. After that, I have no idea what to do - dump and try to buy them back cheaper or hold like hell?
I'm a really bad trader, seriously. I should have just held BC instead of trying to improve my positions, I should just do the same with this coin - just don't want to get buried in a massive dump.
You said it yourself, if you're bad at day trading then that means you are a fundamentals investor. You should be happy that you are invested in a coin that you know is a good coin. Day trading is a totally different skill than being able to recognize a good coin when you see one.
What to do to get your % on your stake ? Is it ok to locked my wallet and wait ? Or has it to be unlocked to receive POS ?
If it has to be unlocked, after how many days it has to be unlocked before i see some coins comming in ?
I saw 3 days , but do you actually see it after 3 days ? And how many % will come in ?
You have to unlock your wallet once every 3 days for a while, to let them stake. I got some minted Cinni already

Every 100 day you should send your Cinni to an other wallet, to reset the coinage.
You get 3.5% a year, so probably like 0.02876% every 3 days.
I want to add that it is best to leave your wallet open all the time. Since this is POS you are supporting the network by having your wallet unlocked and open. Also you get transaction fees if your wallet is open.