Hi Adele Grono,
You should be able to do this by adding visibility rules. Create a drop down for each set of choices and then create a visibility rule for each one based on the different value selected in the first drop down. With regard to the numbers of attendees allowed for each choice that is something you will have to manage manually. You could assign people to lists based on their choices which might make it easier to keep track of the totals.
With regard to the numbers of attendees allowed for each choice that is something you will have to manage manually.
Can we have show/hide functionality for an attendee's second choice and use flow boost counter code Sanford Whiteman?
Sure, the two can work together seamlessly. The per-course attendee cap(s) can be enforced whenever a course is available. That is, the no-two-courses-on-some-day rules and the course-is-full rules both are in effect.
However you will need JS to power this solution. It can't be done with Visibility Rules.