1. What do you think about my plan in general?
Your plan is a good idea but what i will only like to adjust about the whole thing is the need to only maintain two portfolios to your bitcoin, having up to 3 wallets or means you adopt in storing your wallet could pose a little way for vulnerability because of the numbers in consideration so that you don't mix things up and easily make mistake others cab take advantage of, have either hardware wallet or use a bitcoincore client to run a full node and additionally use a centralized exchange with hot wallet to perform your exchange.
2. I currently have paper backups and I plan to change my backups from paper to metal, especially for my hardware wallets. Do you agree with that?
Good idea as well, it's a good recommendation to take and follow, back up your seeds in a more secured ways than just on an ordinary paper which can easily got damaged by water except if laminated, but the safety storage to keep it is another challenge, so the best is to go for the metallic sheet and got it encrypted
3. Would you want to share what you do and how you organise your Bitcoin?
I make use of electrum wallet on an air gapped device and i ensure that i don't use my device for other internet browsing purpose than handling my bitcoin wallet.