You are free to use as many modules as you want. Then you will implement beta in Kit hardware and run it. In order to do 128 bit integer addition, first you need to decide on how you are going to represent a 128 bit integer. You can come up with your own way of representing a 128 bit integer. Normally such integers are split across several registers or data cells.
Addition is done for each part and result is put across a group of registers.
When putting the result together, you also need to see if there is any carry from one part of the sum to another. In order to do this 128-bit addition in kit hardware, you have to directly write the summands to data memory using JTerm interface. Then you can use State button to upload the file containing the summands to data memory. So you can just do a simple arithmetic to retrive individual digits. Now you have to figure out how to convert that bytestream back to 1234.