Holy crap. The most expensive part of your build should be the cabinet. Buy a nice Samsung TV that has the connections on the side. The computer should be an old one that someone you know is trying to get rid of for cheap. The speakers should be a set of these. https://www.amazon.com/Logitech-Multimedia-Speakers-Mobile-Devices/dp/B00KK9481I/ref=sr_1_15?crid=21ALHSF0D4Q71&dchild=1&keywords=logitech+desktop+speakers&qid=1595506815&sprefix=logitech+des%2Caps%2C205&sr=8-15
I'm not saying you shouldn't buy an expensive computer. I'm just saying you shouldn't put an expensive computer inside an arcade cab because you'll get annoyed when you want to sit down and play a nice PC game.
I like my desk mats, basically a giant mousepad that stretches under your keyboard.
Havit Extended Large Gaming Mouse... https://www.amazon.com/dp/B01M18UR54?ref=ppx_pop_mob_ap_share
A good laptop stand to elevate it off the desk and open up space underneath.
AmazonBasics Laptop Stand - Black https://www.amazon.com/dp/B00WRDRRWW?ref=ppx_pop_mob_ap_share
Good set of speakers.
Logitech Multimedia 2.1 Speakers... https://www.amazon.com/dp/B00KK9481I?ref=ppx_pop_mob_ap_share
Cable management.
Alex Tech 10ft - 1/2 inch Cord... https://www.amazon.com/dp/B07FW3GTXB?ref=ppx_pop_mob_ap_share
Cable management box doubles as footrest
Anker 4-Port USB 3.0 Hub,... https://www.amazon.com/dp/B07L32B9C2?ref=ppx_pop_mob_ap_share
A good keyboard. I do a lot of CAD work, so prefer a left handed numpad which allows me to keep my right hand on my mouse
Bloody B845 Light Strike (LK) Optical Mechanical Gaming Keyboard – RGB LED Backlit – LK Blue Switch – Left Handed Keyboard https://www.amazon.com/dp/B073X996W6/ref=cm_sw_r_apan_i_SBBQ24WXGFFFE6PGYCE4
Speaking of a mouse, get an MX Master and don't think twice about anything else.
Logitech MX Master 3 Advanced Wireless Mouse, Ultrafast Scrolling, Ergonomic, 4000 DPI, Customization, USB-C, Bluetooth, USB, Apple Mac, Microsoft PC Windows, Linux, iPad - Graphite https://www.amazon.com/dp/B07S395RWD/ref=cm_sw_r_apan_i_EDK7PWYX0SREJR03FN93?_encoding=UTF8&psc=1
Lighting for that vitamin D
Miroco Light Therapy Lamp,... https://www.amazon.com/dp/B081MT6Y5B?ref=ppx_pop_mob_ap_share