For movies I would not be too concerned with the surrounds or Atmos speakers. It might be more of an issue if you often play multi-channel music or have an AVR with Neural-X for simulated surround music, where timbre matching can be more desirable, but many in the forums have surrounds from different manufacturers. You can still take a staged approach and change the front stage first and decide later whether the surrounds will need upgrading too, unless you think any potential mismatch will be very annoying.
In my own system, I don't mind having different surrounds, but I found it annoying to have a mismatched center because the dialogue would change tone moving from L to C to R. Will the dealer let you try the speakers in house? You could consider replacing the mains and saving up for the matching center.
As to power requirements, you can look in terms of sensitivity and volume. The RC-35 is rated at 98dB at 2.83V which is on the high side, so the Klipsch do not need a lot of power to play loud. The Aria 926 is rated at 91.5db (92db for the 936) so will need more power to reach the same SPL. You can use an SPL meter app to measure your typical listening levels and use the web site below to estimate the power needed to drive the speakers to that level:
https://myhometheater.homestead.com/splcalculator.html
92dB is still relatively sensitive and should play pretty loud. Even if you can't listen to the Focals and B&W in the same store, for that kind of money I would want to demo both. Bear in mind that the impedance on the Focals dips down to 2.8 ohms, so check that your amps can handle low impedance loads.
