@clyde I spend my new years eve playing "Aye, Dark Overlord!" with a couple of close friends (whom were all tested prior). It's a lot like pen and paper role-playing, but sort of a light version. I loved it!
The RetroPie SD image is built on top of Raspbian lite (Raspbian without the PIXEL desktop environment) RetroPie can also be installed on top of the full Raspbian but you can't run Retropie and PIXEL at the same time, you will need to logout of the PIXEL desktop environment in order to run emulationstation and the emulators RetroPie installs.
This video explains the majority of arcade joysticks on the market.
A extremely detailed website about joysticks and button layouts is slagcoin.com. Its creator approaches the topic with almost scientific commitment.
Another thing about the buttons you're considering: They have microswitches that make rather noisy clicks every time they're pressed and released. If you don't like that (I don't), you should look for leaf switches which are somewhat less durable but nearly inaudible. Alternatively, there are "silent" microswitches that are promoted as (nearly) noiseless, but they are more expensive and I don't have any experience with them.
The choice of speakers depends on your quality standards. I didn't like the sound of cheap speakers. Now I'm happy with wideband speakers for 30€ each. See my Asteroids-themed cabinet for a picture of them where you can see their brand and model.
If it helps, I have been occasionally updating the WIKI page for Keyboard Controllers. This has not been "pretty-ified" and copied over into the main Docs menu like most of the other wikis. It is a work in progress that can help folks using an IPAC or other keyboard controller (or even GPIO) hit the ground running. Several of you have helped with the details. Check it out if yours is a controller that sends keystrokes.
I see a lot of Zero Delay usage, maybe because they are abundant, inexpensive, and relatively easy to setup. However, I don't know much about them. If we have an expert on them, we should setup a wiki page for this controller too.