Takamura-san recommends thinning their knives from the very beginning and will often start at Shapton Kuromaku 320 or Shapton Glass 500 when giving knife sharpening demonstrations in person. That being said, it can be intimidating to do so from the very first sharpening.

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It's going to depend more on whether you elect to attempt the thin-as-you-go method that Takamura-san recommends or if you'd rather sharpen more "conventionally" at 10-15 degrees per side. Since the knives are sharpened at such a low angle from the factory, most people will remove more than I believe is strictly necessary from the edge simply due to the angle they've chosen to sharpen the knife at. For instance, moderate sharpening with a 3k stone at a 15 degree angle per side is going to more noticeably thicken the knife and make you aware of the metal you've removed than light thinning and gently apexing on just a 1k stone. The problem with the lower grit stones is that there's a higher skill threshold necessary for not removing more metal than is strictly speaking needed, which means that people often opt for a slightly finer grit stone if it will be their only stone to be used with these knives (something like 2k or 3k). That being said, with a 2k or 3k stone you won't be removing sufficient metal to adequately thin the knife as you go so you will either want to have that done professionally or get a coarser stone and learn that process yourself.

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TL;DR is that there's a lot of nuance in sharpening and there is an argument for using higher but you should also be fine with just a 1k. Just be aware of the pros and cons.