Thanks Malcom thats quite similar to what my process will be. Development of each sub-system will happen individually and inputs/outputs simulated with the dev board bits until I can use the actual bits as it grows into proto stage and then onto proper boards (using PCB train to try and get compact and good quality multilayer boards done) ... I'm really looking forward to starting on a decent development project for my own hobby rather than doing what work place tells me to do =P