Hi @Paul2, welcome to the forum. You’re in the right place 
Yes, but you have some options. One MacOS you can embed Csound into your plugin and then relink the binaries. Then users don’t need Csound installed. On Windows you can just install Csound alongside your plugin if it is not already there.
Not unless you build Csound and Cabbage yourself with 32bit support. @richardk did this recently, and posted the binaries here. So it can be done, if you really need it.