After 25 years, my music setup in my office is breaking down and I am looking to replace it with a decent stereo (not home theater) amp and a set of bookshelf speakers. The main purpose of the setup is playing music, but I will plug the occasional synth in the system as well. Can I do anything wrong?
My background includes a decade or two in the hi-fi business, yet I would strongly encourage you to consider speakers with a large-enough woofer where possible, perhaps an old vintage pair of Yamaha NS-1000s or the like, even if your office is relatively small-ish as mine is (5m x 4m). There are plenty of other options as well that can be made to sound quite good with a bit of extra setup.
Bookshelf speakers are, in many cases, much more demanding of their associated electronics, yet they can never reproduce the fundamental tones generated in the lower register by most electronic musical instruments. For an electronic musician, I feel, they're a lose-lose proposition as they fail to provide a reasonable sense of scale relative to their cost.
I'm spoiled to have a pair of three-way hi-fi loudspeakers, each with a 15" woofer, driven by 150W American solid-state mono amplifiers / 50W British integrated amplifier, depending on the mood.