All yes. For 2: the addresses are always derived in the same order.
Use the 3rd address and you need to add 3 addresses when restoring to see the same one.
You have to remember which crypto you had though.
For 5: yes and no. For some coins you need a different UI because it is just it not supported in ledger live but the ledger itself can communicate with the UI. Coins are never „downloaded“ to the ledger.