1. Since a special lightning wallet is required to receive bitcoin via the lightning network, does that mean you can never use the LN to move bitcoin directly
into a hardware wallet such as Coldcard or Trezor? If so why hasn't any hardware wallets implemented LN? Technical limitations?
Because hardware wallets are offline wallets. Lightning network has to do with online.
Is there any reason why anyone would choose LN over the main bitcoin network? I know LN fees are much cheaper but if you can't use it to move your bitcoin
to and from a standard hardware wallet then what is the point?
Some people use it to hold little amount of money.
It is available on some payment options.
For noncustodial means of using lightning network, people can open and close channel and use it to mix coins.
2. How secure are lighting wallets? Are they considered hot wallets?
They are hot wallets.
3. Can LN be used to actually buy and sell bitcoin or is it only a means for moving BTC between wallets?
Why not, if the buyer and seller agree to use it.
4. Are there any bridges available (lightning chain to BTC chain and vice versa)?
If you use wallet like Electrum, you will move coins from on-chain to open a lightning channel. Use it for payment and also use it to receive payment. You can move your coins back on-chain. Both opening and closing channel will require on-chain transaction fee which is the transaction fee paid to miners.
5. What are current practical use cases of lightning network (not just theoretical)? For example, are people currently using LN for international remittances
on any significant scale? Do any retailers use LN to accept payment for goods and services?
As lightning network adoption continue to increase little by little, it is getting accepted as payment option. Also if you know how to use it to pay and the receiver knows how to use it to receive, you can use it for remittance.
6. Is lighting network still in very early stages of adoption? LN is a great idea but so far adoption and real world usefulness seems very limited.
The adoption is slow, but still increasing. Let us expect more to come. But the reason for the slow adoption is because it is difficult to set up lightning network on wallets that you will open and close channel. But easy to use lightning wallets are existing now in a way the you will not have a node or open a channel. More exchanges are supporting it now also including Binance, OKX and some other exchanges.
