Buying speakers first IS, I think, the best way to go about it, but I might go even further and say that it's really the speaker/amp pairing that may be the most important...that is, it's not quite like buying a source, which can be thought of pretty much independently. Some speakers, perhaps especially those that may be thought of as at least somewhat difficult to drive, may show a common preference among their owners as to what amps the owners prefer to use. What are they? You just poll them in a forum to find out. What do Maggie owners use, or Theil or B&W?...you can just poll them to get an idea. Sometimes dealers are known to come across uniquely good speaker/amp combo's that may or may not be generally known among buyers - you should always venture to pose the question to the dealer, you never know. Some speakers, during their development, were "voiced" with a known particular amplifier. And some speakers, for whatever reason, may not seem, or be known, to display any noticeable preference for an amp...which may suggest to you the speaker may either be a good value in that it may sound excellent with a wide variety of amps - or, may merely sound decent with any amp, but may not necessarily produce genuine magic with any of them - that's Your call, of course, but attempting to know the ins and outs of all that sort of thing is where direct experience comes in and, unless you talk to others who've been down a road or two on that before, you may just have to trust your own instincts...or borrow equipment. If dragging your Gallo's to a dealer is a bit much (and I think anyone could agree that it is), maybe you could arrange to bring home an amp. Talk to a dealer and ask what all may be required to make that happen (possibly some sort of deposit). Not everybody here will likely agree with me about the relative importance of speaker/amp matching, but that's my 2 cents.
Finding the right speaker among wildly varying listening circumstances may be a bit like being on the lookout for Miss Right. The most important thing is simply to give yourself an indefinite amount of time and to do a lot of looking. You will come across a lot of candidates that will have their pluses and minuses, but when you finally meet the right one you will know it! THAT'S the one you want! ;)