I bought some bitcoin on Cobinhood. Can I send them now to the desktop wallet of bitcoin.org, and leave it there for 5 years or longer, without caring about it in this timeframe? Or is it neccessary to update the wallet from time to time? What happens when Litghting-Network or a fork is coming, do we have to update something?
Yes, you should send them to any wallet of your choosing that you control completely (by means of seed or private key)
make a backup copy of your wallet data, make extra backup copy and another extra extra copy
better safe than sorryalso a good practice to create different type of backups: wallet file, recovery seed or private keys
then store them in different places or techniques: usb stick, paper wallet, zip password protected file an etc
you can even hide it (zip file appended) in an image
and use it as your desktop wallpaper