Just to be clear, you should use a cassette with the same number of cogs (9 speed, 10 speed, etc). And yes, it’d be simplest if you also use a cassette with the same tooth range (e.g., 11-34). That’ll probably be fine for both kinds of riding, especially if your bike has a 2x drivetrain. One would need to know your drivetrain specs to advise further.
For the brakes, the best thing would be to find a 700c wheelset that uses exactly the same hubs as your 650b wheels. Any other hubs might require minor adjustments of the brakes when you swap wheels, if the rotors don’t end up in exactly the same position on the two wheelsets. My instinct is that centerlock vs 6-bolt won’t necessarily matter for this, so if you can’t find identical hubs, it should be fine to get 6-bolt hubs on the 700c wheelset. (Indeed, that might even have advantages, because there are shims available to tweak 6-bolt rotor spacing, e.g.,
https://bikerumor.com/2015/11/11/jus...otor-shim-kit/)