TLDR: whatever setup makes you smile, and does what you need is the best setup. My only suggestion though would to use the Server versions of Windows, and not the desktop version.
Cpu Resources: yes windows has more background stuff that uses more resources, but let's not lie to ourselves - this isn't the 90s. Even a windows desktop now days runs at like 2% cpu. You got plenty left over
Memory resources: yeah windows uses more do to unneeded services, but RAM is cheap enough and easy to add.
Update reboots: windows desktop OS will automatically update and reboot by design. mS did this cause basically they were sick of their OS being called insecure , when in reality people were just not updating. There are ways to trick windows to not do this (like setting your NIC as metered), but you can't depend on that. You don't have this issue with Windows Server OS.
Storage options: windows server has a robust storage solution despite what some say here. I manage a server with around 48 drives in it with petabytes of space. Additionally it will allow you to use SMB/cifs , iscsi, and NFS shares.
So yeah... Windows costs more, and is a little more bloated.... But if you're comfortable with that trade off for ease of use, that you go for it! Ultimately in the long run you'll learn what works for you, and what doesn't - but as long as you enjoy it, and are proud of it... That's all that matters.
The only issue hosting your own non-bisiness mail server is that a lot of internet providers block incoming port 25, so you may not be able to recieve incoming mail. Getting a reverse DNS setup may be an issue as well which will bring your mail score down.... But you can increase the score with SPF and DKIM implementation.
Just make sure that you secure your server from unauthorized relay or you'll be blacklisted in no time.