Yes def a touring machine and 25k Easiliy doable with planning, but the open water does add another element, I have been 10km offshore and it's very lonely out there by yourself.
Along with the other safety items above, choosing a kite will also be a big consideration The kite size you choose in the morning has to last you all day If the wind picks up and you have a big kite you gunna be going downwind!
But if the wind drops you could be swiming.
I did this 70km run on the weekend in a charity sailing event, Lots of wind shadows, started on a 15m foil kite and not long after start we had 20 to 25 so heading upwind you kinda get a bit stuffed ;)
To minimise the risk, Summer time when lots of other boats on the water would be good, but when it is windy they dissapear but at least with a foil board you can still go when its not that windy.
This 70km took me a little over 2 hrs but didnt have good upwind angles when over powered and got lofted a few times in the gusty areas :(A big open bay should be a breeze