I learned something new in the past week: back in the early days of Bitcoin, coins were sent to pubkeys instead of addresses. This makes it impossible to sign offline using an SPV wallet.
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Can I just check these are the right core clients for each:
BCH:https://bitcoincashnode.org/en/download.html
I think this one is fake, it should be https://electroncash.org/ (see https://bch.info/en/wallets, which came from https://coinmarketcap.com/currencies/bitcoin-cash/).BCH:
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XEC: https://download.bitcoinabc.org/latest/
BTG: https://bitcoingold.org/downloads/
BCD: https://www.bitcoindiamond.org/download/
I think this is okay.BTG: https://bitcoingold.org/downloads/
BCD: https://www.bitcoindiamond.org/download/
Note that I wouldn't trust the "official" websites either! Don't risk running that software on your normal computer, Forks were meant to make the creator rich, not you. So keep it offline, and keep it away from your normal system.
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BTW, it looks like BCH and BTG can be sent to a Ledger wallet once set up for those coins, but not XEC or BCD
Correct. My advice: get rid of them 
I'd gladly provide my services for this (it's been a while).You forgot BSV in your list. It's the most annoying one with the shittiest wallet software, but still worth something.
For privacy: if you link any of your addresses together on a Fork-chain, that's basically the same as linking them on the Bitcoin chain. If you're okay with that, you can forget about it.