Lots of great advice here. I'd add the following: newcomers should decide up front whether authenticity or versatility is more important, because you can't have both. In other words, do you want to faithfully replicate the original experience of a small number of games, or do you want to sacrifice some of that nuanced authenticity in the name of having a more general purpose gaming rig that can passably play a much broader catalog of titles?
The "right" answer depends 100% on the user. Me, I'm glad I followed the latter route, because through experience I've learned that there are hundreds of games that I can thoroughly enjoy on my cabinet, even though they originally shipped in boxes that look quite different from mine with controls that feel quite different from mine.
Real arcade games didn't have cup holders.
Which is why people don't tend to put cup-holders on real arcade games. But a generic cabinet stuffed with a PC that runs emulators is inherently not a real arcade game, so cup-holders are very convenient and make a lot of sense in that case.