You can't really mess up a lot.
The most important thing is to transfer your coins from the highest to the lowest value. This means BTC first -> BCH -> ...
Afterwards, if you always send funds to an address you own, you don't have to worry about your transaction being replayed.
Even if someone is going to take your transaction and replay it to the other chain (e.g. from BCH to BSV), the coins will be sent to your address.
Such an replay attack can only be 'dangerous' if you send funds to a different person, because that person can replay the transactio and also receive funds from the other chain.
But since this is not the case here, you don't have to worry about an replay attack.
I wouldn't trust github anymore, only use the real electrum.org. There have been fakes, and I'm not sure which one is real on github.
https://github.com/spesmilo/electrum is the one and only real github repository from electrum.
In my opinion, you can mess up a lot.
1) There's tons of crapware taking advantage of the assorted forkcoin clients as "free money" is too tempting to not get the thing done and dump said forkcoins
2) You can ruin your privacy when you are moving your BTC to import the private keys into the BCH/BSV clusterfuck
In order to avoid 1, use an VM, ideally use a different device, and download the official full client. Double check checksums.
In order to avoid 2, use Coin Control to properly move inputs.
I have always been torn about forks. It is our duty to dump the shitcoins to 0, however it is just insanity to move your entire f*cking stack if you have tons of different transactions and want to avoid 2). Result, I haven't even sold any of the shitcoins yet. Doesn't seem that I need to, they continue tanking as predicted.