--snip--
So what would be the safest way in step 5 then ?
lets say for example im taking out some of these forks
http://www.findmycoins.ninja/didnt claim any of them not even BCH
so i need to download each individual wallet of a forked coin, upload the private keys there and do it over and over again with each coin ?
yes...
find the most expensive coin, find the list of supported wallets for said coin, check if the wallet is safe (check if there are scam reports about the wallet OR the coin for that matter). If it's safe, run the wallet, import the private keys from step 4 (only the private keys belonging to an address that was once funded are needed, altough it doesn't hurt to import the full list if you're unsure), spend altcoin (send the altcoin to an exchange if you want to exchange it for BTC or to a new, clean, wallet if you want to hold on to the altcoin).
IF the altcoin has a forked version of electrum (a lot of them do), i'd prefer the forked version of electrum over the forked version of core... Core needs to sync the full blockchain and it takes a long time to do this... There are technical sollutions to avoid having to sync the blockchain for each altcoin, but this makes things even more difficult.
This clearly proves why you need to EMPTY out the original trezor wallet and move all BTC to a new, safe, wallet before you start importing the seed in electrum, exporting the private keys from electrum or importing the private keys into an altcoin wallet... Why?
Because:
1) if you're importing trezor's seed in electrum, you're basically typing a seed phrase that's meanth to be offline 100% of the time on an online machine. There is no guarantee that electrum is 100% bug-free, there is no guarantee your PC is 100% clean, there is no guarantee you have the "original" electrum version... As soon as you type the seed on an online machine, there is a chance somebody malicious gained access to the seed phrase
2) if you're exporting the list of private keys, you dump them to a textfile... There is no guarantee your PC is 100% clean
3) if you import key into an altcoin wallet: those wallets are basically forks from bitcoin wallets, these altcoin wallets aren't always vetted in the same way the originals were once vetted... There is no guarantee the developers haven't added a backdoor.
Even if you don't care about any of this, some forks might not have replay protection! So, it's always a good idear to make sure all the unspent outputs on the bitcoin blockchain have been spent before starting the procedure...
I've once made a nice graph to explain replay protection... here it is: (copyright: me
)