Hi Ayre,
You may find the MC812A4 to be a good candidate for your project. It is powerful, easy-to-use, and meets your requirements for memory-mapped I/O and potential RAM and Flash size. Have a look at some of these products to get an idea of what is possible:
http://www.technologicalarts.ca/catalog/index.php?cPath=22_33It is especially easy to add external memory and memory-mapped peripherals.
Best regards,
Carl Barnes
www.technologicalarts.com