This is not always the case, but in general (for me at least):
Warm... something along the lines of NAD, Arcam, Creek, etc. (including most vintage gear)
Neutral to Bright... something along the lines of Cambridge, Cyrus, Rotel, etc. (including flat-voiced pro components)
Please note that not all warm gear sound the same, and not all bright gear are alike. They all have different characteristics, and a certain bright amp might not work with your speakers, yet another one might, for example. The actual performance of each component typically varies beyond the posted frequency response and distortion numbers from the manufacturer, because of interaction between components (speakers don't introduce a constant impedance and are reactive loads, for example). Coloration also accumulates as we go down the signal path, plus individual preferences and room acoustics also vary --- so it's best to test out different combinations (unless you plan on relying on processing, which is another way out).
Amp capacity is beneficial if you need it. It gives you dynamic headroom, and the ability to play louder. If you're playing dynamic material at elevated levels, a weaker amp may not be sufficient (especially in a big room). The quoted range of 20w-100w just gives you a rough idea that most amps rated 20w and up can sufficiently drive these speakers to reasonable levels in a typical application. Whether this meets your needs will depend on your demand on the gear.
I know I should've asked this beforehand, but are you building a music system or a movie system?
