This is still not a bad plan. Adding a low amp AC 110V power to a single light fixture in center of the basement room is trivial IMO using a bulb adapter with 2 110VAC plug in ports is as simple as unscrewing the bulb, screw in the adapter then the New Led bulb and plugging in a power strip over the the shelf for the PC.... I doubt you will over load the 15 or 20 amp Light circuit.
https://smile.amazon.com/Simba-Lighting-Adapter-Control-Basement/dp/B07X64HBMV/ref=sr_1_1?crid=386Y1YK1D9L56&keywords=110v+ac+bulb+adapter&qid=1649870634&sprefix=110+vac+bulb+adapters,aps,590&sr=8-1
The hole in floor, once cables are in, can be easily pest proofed with a wad of insulation or even cotton. I would spray most any home use, pet safe, pest killer on the shelf, Wad, and a foot or two on the cables. In out Texas rural house I swear by Demon WS2 from Ace hardware. A two pack of water soluble packets in $15 or so and mixes into a 1 gallon pump sprayer. Enough for the perimeter of most homes. I only use it inside where my 4 dogs cant lick at something. This stuff kills all ants, spiders, and roaches. They rarely get more that a few feet before very dead and vacuumed up.
https://www.amazon.com/Insecticide-...r_1_2?keywords=demon+wp&qid=1649870747&sr=8-2
The shelf is easy too. I assume open floor joists over head in the basement so three 3/4Inch thick plywood (ugly but and grade will work as basement should be relatively dry. The Joists should be 6 inches deep top to bottom and every 16 inches on center. Tower pcs at tall and others are wide but low. I would make my shelf slightly below eye level and wide enough and long enough for all the components.
So 3 ply boards all the same width as the shelf ---say 24 inches (there is a reason for 24")
2 will go from you desired shelf height off the floor all the way up to the floor.
1 will be between these two as wide as needed ---
In my head I see 2 PCs side by side and one UPS* between them My desk top is 11 deep by 21 wide by 4 tall.
with a gap for air between both of 4 inches I need 21+21+4 and another 2 4 inch gaps for the 5 inch wide UPSso
21+21+4+5+4+4=59 ..... remember the joists are 16 inch on center....so inside of left joist is X inches from the inside of the joist I need to the far right joist. I think I need to span 4 floor joists with my shelf to get a bit bigger than the 59 inches of shelf needed. Some where between 62 and 64 inches.
A 3/4 inch ply shelf 24 deep and 64 long will hold that weight with out sagging
You can buy ready dimensioned solid wood** or a sheet of ply at Home depot / Lowes type stores at reasonable prices
Since my shelf need to be wider that 48" I can consider 24 in by XXX long solid wood in the dimensional wood isle... they sell in 1/2 in and 3/4 inch stuff of many soft and hard woods... But a bit pricey depending on pine vs Red Oak...both will work
Becaus my shelf is so long--- 3/4 inch ply is not really a good choice unless I can use the rest for some other project. The cost of PLY is still too high IMO
you need some
https://www.amazon.com/s?k=4+inch+l...887791&tag=googhydr-20&ref=pd_sl_7xr9zrs017_e
and you need wood screws long enough for the bracket and through the shelf sides into the 2x6 floor joists
The one down side to stealing 110VAC from light socket....MUST leach light switch ON 24/7 (taped ON) and use pull string to get light