Long time ETH holder, first time self custody

I've had (a very small amount of course like $2) ETH for quite a while, but I've always held on an exchange (staking currently), and after nearly getting burned I'm done with them. I recently got a Trezor and want to self custody funds, however I'd also like to convert to rETH to get some APY. I've been doing some research and learning the basics, though there is a lot of info to take in here and trying to figure out what's best, and how to not accidentally screw myself and lose any coin in the process.

Are there any good learning materials to the basic stuff to know?

Some of my initial questions are stuff like:

I hear L2 is ideal for lower fees, should I be converting my ETH directly to rETH, or first converting the ETH to L2, then to rETH? Can L2 ETH always be converted back to L1?

If I happen to have L2 ETH and I accidentally send it to an exchange's L1 address, am I loosing coins, or are there checks and balances in place to prevent mistakes like that from happening?

Or If I'm swapping ETH to another coin like BTC, does it have to be on the main net?

Is there a smart way to test out and learn how this all works hands on? Like should I test with small amounts of tokens, or use Testnet?

Sorry if these sound like dumb questions, but any help is appreciated!

As always, PM's are ignored.