So I have an old laptop I want to dedicate to store coins that are not compatible with hardware wallets. The wifi card takes about 30 seconds to unhook, so the plan is get my wallets setup and leave the laptop offline until I want to sell/trade. I know this isn't the absolute most secure way but feel it is a good compromise of convenience and security (especially compared to just storing in wallet on gaming pc). Was wondering if anyone else is doing this and if so how they went about it as well as had a few questions.

1. Ubuntu or windows 7/10? I know there's a lot less malware out there for linux though I like the ability of windows to do full disk encryption and am also more familiar with windows.

2. Should I connect to the internet to update OS/download wallets after installing the OS and then go offline to setup wallets and backup private keys or should I get the wallets setup (transferred on thumb drive from potentially unsecure computer) and keys backed up before the laptop is ever connected to the internet and then go about updating the OS?