Yes, assuming the voltage ratings are the same; more watts = more amps at same voltage, and more amps at same KV = more torque.
Yes. Until you hit max RPM of course. Lower KV = more torque per amp and lower max RPM.
Sorta - field weakening exists; if you can find a torque curve, the point at which the torque begins to decrease (often the point where they declare 'peak horsepower') is the RPM you could use for KV.
Just a note about Kv: it really doesn't apply to series-wound brushed DC motors, and is essentially never given as a specification for motors suitable for car-sized and larger EVs (even in motor types where it would be reasonably applicable).
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