If the cabinet has an existing monitor & speakers in it, I say use em. I have 4 cabs I saved from the dumpster over the years, all running either the original arcade CRTs or old TVs (which aren't that great, but hey they were free... still looking for original CRTs locally to replace them). All 4 cabs use the original speakers and power supplies.
Since you're planning to use a Raspberry Pi, I suggest buying a Pimoroni X-Hat for it:
https://shop.pimoroni.com/products/picade-x-hat-usb-c1. It has a built-in amp with stereo out. Not powerful, but plenty of juice for powering arcade speakers. Unless using HDMI or the GPIO, the audio out of a pi can be messy, but the audio is routed through the x-hat, so it's nice and clean
2. It has a built-in power switch and inputs for graceful power-downs
3. It has inputs for coins and other admin functions
FYI, there is a dedicated board here for raspberry pi:
http://newforum.arcadecontrols.com/index.php/board,57.0.htmland one for linux:
http://newforum.arcadecontrols.com/index.php/board,39.0.htmlThe content in those 2 boards often cross over.
As for the Joysticks and buttons: I've never used any of those kits, though I've seen others here with knowledge of them. I mostly buy my parts, including joysticks, buttons and encoders from
Ultimarc:
https://www.ultimarc.com/GroovyGameGear
https://groovygamegear.com/webstore/T-molding.com
https://www.t-molding.com/Paradise Arcade Shop
https://paradisearcadeshop.com/Welcome to the board and to the hobby.
Also, you may find this doc I maintain for my own reference useful:
https://github.com/mahuti/arcadepi Lots of obscure solutions to weird pi-related problems.