It will help you considerably if you don't think of this as "converting to Shiny format" and, rather, think of converting your logic to R. Then you put a Shiny UI around some R functions.
There is no magic bullet. You are porting from one language (Excel) to another (R). In my experience, the work flow looks something like this:
- Determine the input data sources and make sure you can connect to them from R and get the needed data
- Document the logic of the spreadsheet. Write down what it does and why.
- Determine from the above documentation what functions need to be written... probably not a full list, but some stuff will be obvious.
- Incrementally write each function in R, test it and make sure you get what you were expecting.
- Create each visualization you will need for your output: tables, graphs, etc.
- after all that is created and tested then wrap Shiny around the whole thing.
If you have some specific questions about mapping excel functions to R, feel free to ask.