As you can see from the varied responses you have received, opinions on the subject are as varied as the number of enthusiasts out there. So I'm not going to suggest any specific speakers to you, or suggest that you buy new or used, or urge you to start with some piece of equipment other than the speakers. But as one who still remembers being a newbie myself, some practical advice:
1. Loudspeakers are a good place to start when upgrading, because then if you later upgrade electronics you'll be able to hear and appreciate the difference. And loudspeakers are the one kind of audio gear where it is still largely true that you get what you pay for -- generally, with reputable brands a higher price point will get you better bass extension and better imaging, at the very least.
2. At any given price point, monitors are probably going to have an edge with imaging, but floor standers will likely have better bass extension. And remember with monitors you will usually need stands, so you have to factor them into the total price.
3. When setting your budget, don't buy anything you can't afford to replace - accidents happen, and as I am sure you know, warranties don't cover accidental damage. So, if your upper limit is $3000.00, for example, and it took you years to save that much, you may want to limit your purchase price to about 60% of that amount -- otherwise, you could end up staring at expensive paperweights.
4. Since you are a musician, in particular, and new to the hobby, I would urge you to not purchase speakers you haven't heard. Do some research in your price range, and then seek out dealers that sell brands that interest you, and listen, listen, listen. Be sure to take your own music with you -- pieces you know well. Dealers tend to have carefully chosen "demo tracks" intended to make almost any speaker sound good -- you want to play and listen to the kind of music you like. I once discovered that a pair of"demo" speakers a dealer was urging me to consider had a damaged woofer only because I had brought along music I knew well that included organ pedal notes (the dealer replaced the woofer, and I ended up buying the speakers).
5. ¥ou can get into some really impressive arguments over the question of speaker cables -- I would say to avoid fancy speaker cables, at this point, and concentrate your money and effort on the speakers -- if high-end cables do make a difference (and boy, can you start an argument by introducing that topic among audiophiles and electrical engineers), it is incremental.
6. Keep your listening space in mind when looking at speakers -- if the space is relatively small, in particular, consider how the speaker is going to fit in the room and how much flexibility you have in placement. Smaller rooms and fewer placement options often make a monitor, rather than a floor stander, a better choice because they tend to be more forgiving and less boundary-dependent.
7. Most of all, take a little time and have fun looking at the options. As with many things the journey is at least half the fun.
