TTaiiLs

Yes, sorry for the unclear wording. I dual boot Fedora Linux and Windows 10.
 
Gaming on Linux is mostly fine, but for things that have wack DRM (i.e. basically all non-steam games) i find that Windows is just less hassle 

CSM (Compatibility Support Module) which emulates the old BIOS was designed for legacy hardware who cannot operate on a modern system.
Having this option enabled means Windows 11 and later won't be supported on your system.

Yes, that is because the OS' you have installed are setup in Legacy and not UEFI, your new computer is UEFI, you will need to see if your board supports Legacy or CSM or you will need to do a UEFI conversion of Windows in order to get it to work on the new computer. It can be a little complicated, next option would be to just do a fresh install of Windows which may be best anyway since you've made major hardware changes and may have driver issues on the old install regardless of if you convert it successfully or not.

Your options are a used i7 for a fairly minor performance increase, or sell everything (except for maybe case, storage, GPU, and PSU) and start a new system.

If you can't move to a new platform, try overclocking the 4690K if you've got at least a decent aftermarket cooler and/or look for deals on used 4770Ks and 4790Ks.

NICE, have loads of fun!!!

No you shouldn't be able to damage the ports, they're isolated with very small transformers.
You probably created a loop, sort of like taking a cable from a switch port and plugging it back into another port of the switch.
I guess the switch or router in your building probably disabled the port to protect itself from sending data packets in a loop for eternity.

What is connected on the other side of your wall port? If this is your internet connection provided by your apartment complex, dorm, hostel, etc, then probably the port got disabled by your router’s LAN being detected as a rogue router. You’ll need to call the provider of the network to have your port enabled again.

Not worth.

Don't bother going from a 4 core processor to a 4 core processor, they all have similar flaws these days. Save up for a better upgrade, or just wait for a new generation of CPUs if you aren't happy with what's currently on the market.

No, I do not think that the upgrade would be worth it. If you're going to upgrade, try and move up in core count or at least get hyperthreading. The R5 2600 would be a perfect upgrade, but the R5 1600 or (if you must have intel) the i5 9400F would be fine as well. 

They're both 4 core 4 thread processors with the 9100f having a faster core clock and being much newer. If a possible 9-10% performance increase over the 4690k is worth the cost of the upgrade to you then go for it. If I were you I'd just overclock the 4690k and gain the extra performance that way without spending extra money for basically a sideways upgrade. If you are looking to upgrade I would suggest going with a Ryzen 3000 CPU/ Platform upgrade.