Will my ability to play games be significantly affected compared to Windows?
Depends on the game. In general no, unless it has kernel anticheat, which Linux will not allow because that's a glaring security risk.
Can I mod games as freely and as easily as I do on Windows?
Yes.
If a program has no Linux version, is it unusable, or are there workarounds?
Most Windows software can be run on Linux using Wine. But there are advantages to using Linux-specific alternatives - they are often lighter and faster.
How do OS updates work in Linux? Is there a "Linux Update" program like what Windows has?
Yes, each distribution has its own update tool. They also install and update software (like in Android, where Google Play installs and updates all apps and not just the OS). No need to download exe files from random websites.
How does digital security work on Linux? Is it more vulnerable due to being open source? Is there integrated antivirus software, or will I have to source that myself?
Linux is generally much more secure than Windows, because it is open-source. Most internet servers and supercomputers use Linux partly because of its security.
Are GPU drivers reliable on Linux?
Nvidia is notoriously bad but getting better. AMD is good.
Can Linux (in the case of a misconfiguration or serious failure) potentially damage hardware?
No.
And also, what distro might be best for me?
Linux Mint. It is stable, reasonably up to date and does not make confusing changes every update. It also tends to work on most systems.