Trust me, I'm fully aware of all of the trouble with getting RPCs to work properly. I still think that it is easier to do that work after you have the original non-rpc version as a reference.
Yes, but making those module boundaries loosely coupled and sharing information only through their interfaces will go a LONG way towards enabling you to remote the call at a later date. The biggest mistakes that prevent remoting a module have to do with requiring context that is not part of the interface of the method call (or having a very chatty back-and-forth, but that is less common.)
