Glad you are joining the project!
As mentioned on the product page, yes, the B104 can be shipped with ISO layout, but you have to purchase any MX key set if you do not want to use the key set offered by the project. I do not offer any of these other key sets, but just about all of the normal mechanical keyboard MX key sets should work on the new beam spring keyboards.
It is very easy to install the keycaps; you just press the keycap onto the keystem on the keyboard.