I have few questions still, I want to know if connecting software wallet to your hardware wallet gives it the security as intended? If I start using software wallet on my hardware wallet does it add more to it's security? Or it's a bad idea?
You can use it with Electrum, and it is a good idea, as Electrum has more features to allow better control of your private keys and your bitcoin
https://support.keyst.one/3rd-party-wallets/bitcoin-wallets/electrumAs for the firmware update, I have two options, one through SD card and the second through USB connection, which one do you think is better and safer upgrade way?
You can use either method, more details here
https://guide.keyst.one/docs/firmware-upgrade#1cbd53ed0dad4b97a357a51fc5aab3d4