You're kinda going in several different directions here. What's that $550 number for? Speakers, Subwoofer,/receiver? All three or various parts thereof?
anyhoo, here's some general advice:
The front three speakers should match. If you listen to true 5.1 multichannel music then the rear two should match.
If you listen to movies and synthesized multi channel music (originally two channels) then the rears don't have to closely match the front three, but it's nice if they do.
If you like the sound of the speakers, then go for them. Everyone has different tastes and one cannot question someone's preference. What they prefer is the best, for them at least.
ID subs like SVS, Hsu and other companies who specialize in subss tend to ofer more bang, or boom, for the buck than subs from full line companies.
As for future proofing, good luck. Nobody can see what's over the horizon. Three years ago who ever thought of 4k and Atmos?