Fortunately, calibre speaks to both EPUBs and Kindles, and can run a batch job even while you are sound asleep.
Unless you simply can't spare the loss of disk space, it shouldn't be a problem.
My advice is to focus on the features of the different devices available. For instance:
The Kindle is supposed to have a vastly superior dictionary.
The Kindle is simple, no frills but just get's the job done. The Kobos allow you to customize all kinds of things... to death. It could be regarded as simple clutter
and the firmware can be touchy and unstable, whereas Kindles tend to have rock-solid firmware.
Leaving aside the issue of the Kindle's Cloud Collections, which is/was a real PITA but seems to have been smoothed out more or less with the latest firmware.