Is electrum is safe for long term storing?
Yes, it is one of the ideal desktop wallets that's focused in Bitcoin if you don't have other means of storing your Bitcoin through a hardware wallet or any of a kind. There's no problem if you do that and you can basically treat it as your air gap wallet if you ever had a device like a laptop that you're not going to use and just simply disconnect it entirely from the internet.
Can I get hacked ?
Everyone has the risk of being hacked if we're not careful to how we browse on the web. Remember that, depends on the wallet you use. If you downloaded the wrong wallet and it's owned by the hackers that copied an official wallet then you're likely to get hack and your funds will be gone. But if you have downloaded the official wallet, the fate of yours being hacked depend on your browsing activity.