So basically i have to keep safe my words from old ( multiBit ) wallet safe if anything happens .
Pretty much... you'd need to the same for Electrum words as well
And if i did as you said on chain transaction to new ''seeded '' Electrum wallet my fund would become tied to new safe words right? And therefore become differently encrypted and easier to recover in the future ? ( sorry i just done a lot of reading when trying to recover it and got all more confused the more i read)
Yes... if you moved the coins to addresses generated by Electrum wallet, they are then backed up with new words.
And one more thing . I know key words are more or less like a back up but is it possible to somehow back it up otherwise like doing image back up of HDD or similar ways ?
The whole point of the seed mnemonics... aka "word phrases"... is that you can simply write those down, and store them safely and securely OFFLINE. You entire wallet and ALL of it's addresses (old and new) and transaction history can be restored by using those words.
It completely eliminates the need for digital backups of HDD's and/or wallet files... and even allows you to recover from lost wallet passwords (NOT lost BIP39 passphrases tho)... as when you restore from seed you can simply choose a new password
But, there is no reason you can't do HDD and/or wallet file backups if you want... it just isn't strictly necessary.