Getting around character limitation in Data Validation (Source)

Dear colleagues,

It turns out that I am to build a spreadsheet so we can gather interesting data about HR demand management. The point is that, so as to avoid human errors, we would like to have drop-down lists for almost each column. It wouldn't pose a problem if the nested IF formulas that I need to implement in Data Validation were short. Unfortunately, that's not the case, I have indeed 4 categories that are dependent on the value of each other. Since we're on O365, I tried to do this through dynamic arrays. The problem is that you have to generate dynamic lists for each cell, and, as you'll imagine, I don't simply have the time to programme 5000 cells. So, coming back to the original question, do you guys have any thought on how can I do to allow Data Validation to host strings larger than 500 characters? It's the only way I can think of now, since once the string works properly, it'd be as simple as extending the formula and format to the rest of each column.

Thanks a  lot!