Check the jacketed vessel design per ASME sec VIII, could be useful.
i don’t know why don’t you just buy one from the market, it could be much cheaper. Are you required to design it per some code?
There is lots of things that you should take into consideration in the design depending on your point of view and your outcome from the kettle.
This kettle is small and you probably are gonna end up wasting so much money on fabricating it from scratch. And by small i mean by its height, so no standard plate dimensions will give you the results that you are looking for without excessive excess (that’s bad if it’s stainless steel obviously).
Some markets don’t have the ability of giving you the knuckle radius mentioned above, a 90mm knucle radius isn’t excessive but still in my local country you have to pay alot to do it especially with high thickness (above 10mm).
So i advise you to pay for a new one, it will come with the agitator and a supporting structure
and save you some pain.
However you can start practicing your design of a jacketed vessel per ASME sec VIII in the meantime.
Detailing is a hobby,