There is no doubt that Cat5e cabling is the best option for connecting in the home for gaming and video streaming. However, unless you're a licensed cabler who can install network cabling safely (there are power cables in them walls too!), it's not an option (unless you can run under carpet etc.)
1) Stick to 2.4GHz as it is better at penetrating walls and stuff, (but this frequency is more crowded).
2) Buy a really good WiFi card with antennas, then use extension cables on the antennas to get them out of the clutter at the back of the PC.
3) Try a WiFi Range Extender. This will essentially re-transmit the router's existing WiFi SSIDs from a point closer to your pc. Choose a dual band one.
4) Try powerline network gear. You buy a pair of modules that plug into power points and they talk to each other over the ac power cabling. Plug one into a powerpoint near the router and the other near your pc. Then connect with Cat5e patch leads. Should be plug and play.
The best option depends on your individual circumstances; no magic bullet, unfortunately.
One last thing, the safety issue with doing your own wall/ceiling cabling is real. Life and death stuff. Don't do it without the training and qualifications.
I've built 10 or so machines over the years but this site reduces a lot of the research needed.
This build is very similar to a build my stepson and I put together for my daughter. A couple of points to note:
- Paying 5 lots of freight to 5 different suppliers can add a lot of extra cost. Also, some vendors charge outrageously for freight. It might pay to look around to optimise the freight costs; perhaps compare 2-3 vendors as a rule.
- Prices change very quickly so check regularly between build planning and buying.
- Look for specials. My recent build took advantage of great deals on a Cryorig Cooler and an RX 580 card, which saved $100's.