A 4GB usb drive will usually be enough, it just has to fit the size of the .iso you are downloading. You should use Ventoy instead of rufus/etcher, it’s faster and much better when trying multiple distros. Do back your stuff. You usually do not need to disable secure boot.

This would be my summary of the process :

• List all the software you are currently using, and check if they are available on Linux. If they are not, try to find alternatives that are available, and get used to them before switching to Linux. If you don’t find any, you need to dual boot.
• Download multiple live distro .iso, put them all in a Ventoy USB
• Make your bios boot on the usb drive
• Check out the distros you downloaded and find one that a) works b) you like the UI c) isn’t Ubuntu (derivatives are ok)
• Consider your life choices for a few days. At this point MS should start feeding orphans bodies to their AI.
• Copy all your data out of your computer. Be careful. Your browser favorites, non-synchronized game saves, non-synchronized app state…
• Install the distro, usually from an installer in the live environment. Refer to your distro’s manual/a tutorial if you need dual boot or don’t understand the installer. If you do not dual boot, this will delete your windows installation and files. Dual booting is often desired just to keep access to your old system if needed.
• From inside the permanent installation, copy all your stuff back on the computer