For every workshop a different number of ropes is needed, please read the workshop description.
In general, the more advanced you get, the more ropes you will want, and very often need, to use. When you enter the rope-suspension arena even more ropes are needed and wanted.
Some numbers that I found that work are:
4 ropes = beginners set
8 ropes = intermediate set
12 ropes = advanced set
15 ropes = you have elevated to the supreme level 🙂
Having a few shorter pieces rope in your rope-kit can come in handy, ie. 2m and 4m.