Hi. I'm not sure how I can help you with your design. Our USB based oscilloscope is a different type of design. In our design, we do all the data processing on the PC, so it is more flexible and easy to add additional features. For a LCD touch screen oscilloscope you have to think about how to process the data samples. Maybe you could use a single board computer for processing (like rasberry pi) and connect it to our USB based design. All the data processing would then be done on the raspberry which would display the signal on the LCD. On the other hand, if you want the fastest possible data rates then use the FPGA for processing and display the signal directly. Each solution has its advantages and disadvantages. In any case, there are compromises that you will need to take.
Anything is possible, so you have to decide what works best for your design.