I almost always use 1/4" thickness for both open and closed vessels. That seems to be a good compromise between the "wow"factor of lightness and risk of damaging the bowl before completion. I have gone as thin as 0.050" on a few that are made with resin stabilized pen blanks. Photo attached.
Great job, Holger! I particularly like the pattern.
I also like 1/4” as it offers a lot more design capabilities.
I buy a lot of my wood from eBay. If you search ‘thin lumber 1/4” (or 1/8, 3/8, etc) you find a number of offerings that have all been sanded to a perfect thickness. You’ll always find maple, walnut and cherry but often you’ll find exotics as well. It will be shipped in a USPS Flat Rate box which will be fully packed. This will be far less expensive than if you bought from Rockler or the like.
I have a shelf that has 1/8”, 1/4”, 3/8” and is often from different manufacturers and it makes it easy to grab and go.