Regarding my 2nd question, if I send all my BTC balance to the address in my Ledger Nano S with a new seed. Then my electrum would have 0 BTC in it. So I import my electrum seed to other BCG and BCD compatible wallet, then I would still see those fork coins right even I have 0 BTC on that electrum seed?
Yes. You probably have 3 balances in your Electrum wallet:
X Bitcoins
X Bitcoin Gold
X Bitcoin Cash
And I say "probably" because this is only true if you had Bitcoins before both forks.
- If you had 1 Bitcoin while the Bitcoin Gold fork, you now have 1 Bitcoin Gold;
- If you had 1 Bitcoin while the Bitcoin Cash fork, you now have 1 Bitcoin Cash.
When you send all your Bitcoin balance to a new wallet, the remaining coins will stay there. They are all different coins.