iCloud with custom domain

I don't currently have an iCloud mail account. I have a custom domain name and my email is hosted by a web hosting service provider. I am looking to switch to iCloud+ to host my email, but I have some questions about it.

I run Windows 11 on my computer. I use the built in Windows Mail. My email setup is POP3. My incoming email is authenticated by my web hosting provider and my outgoing email is authenticated by my ISP provider. I chose POP3 as I don't need to sync my email across multiple devices, and I keep all my email locally on my machine (it is immediately removed from the server once read).

Right now, I spend around $200 each year for this service, $20 for domain registration renewal and the remainder for web hosting services. Yes, significantly more than I need to for what I am actually using it for, hence the questions.

First question, if I access my email hosted on iCloud.com from my computer, would I still need to authenticate my outgoing email with my ISP? I'm assuming yes, since it passes through their servers as opposed to via an external web site.

Second question, since I already have a domain name registered, can I still use the same email addresses that I currently have set up on my web hosting site on iCloud? I currently use 5 email addresses with my domain name.

Third question, I currently renew my domain name though my web hosting provider. If I choose to switch to iCloud+, how would I go about renewing / transferring /updating it myself since my web host will no longer be doing it? My domain name is due to renew in about 60 days.

Fourth question, since I have to create a mail account on iCloud.com, does this mean my custom domain name emails are being redirected to this address or does it act as a separate email address? I have an email address with my ISP which I redirect to one of my custom domain addresses, but I still need to use it as my outgoing email authentication. What is this email address used for if I use a custom domain?

Last question, has anyone switched to the new outlook email app that Microsoft is pushing out that also uses a custom domain name with iCloud+? Has there been any hiccups that I should be concerned about? Right now, I can't switch to it because my setup is POP3, and it uses IMAP only. So, it doesn't migrate directly, I'd have to start from scratch setting up my email and I don't want to do so just yet.

Appreciate any insights and/or caveats.