Question on Arbitrum L2

Hi, I have some eth on the exchange and I'm thinking to move them to a ledger. I would like to low the gas fee of the mainnet by using Arbitrum, which is supported by my exchange but I've some difficulties to understand how these L2 works.

According with this video (see the link at the end of the post) , once I transfer Eth from the exchange to the ledger on arbitrum I get AETH on the ledger (min. 13.17). If I want to transform them back in ETH I need to use this Hop Exchange (min. 16.25) and to do this I've to pay the mainnet gas fee.

So my questions are:

1. how do I save in gas fee by using this process? It seems to me that I'm going to pay more than transferring directly eth with erc20 because first I have to pay arbitrum fee and then to pay Hop erc20 gas fee (which from the video my understanding is that being an erc20 fee its cost will be the same as transferring eth to the ledger on erc20)
2. the second option would be to keep ETH in the ledger as AETH but...isn't this a less secure asset than the "real" Eth? The difference seems to me like to have real gold or paper gold...is this wrong? What if Arbitrum, which is a quite new thing breaks (from the video my uderstanding is that AETH works only on Arbitrum)? Sorry if my question doesn't make sense but I find really hard to get this thing....
3. Consider that my scope is to accumulate eth by DCA and eventually get some yield. If I move my eth from the exchange to the ledger I would like to use a service like Lido or Rocketpool to generate some yield...so my last question is: can I use these services with AETH, instead of ETH?
4. the last question is: if I do some mistake in setting up the exchange and the ledger on "arbitrum mode" do I loose my eth in the transferring?

This is the video I was referencing to: https://www.youtube.com/watch?v=anK-OFuPwes&t=987s

Thank you in advance!