How to show certain fields on a form based on user selection?

Hello. I am in the process of creating a registration form for an event. It is a one day event which is split into three sessions. Participants will take part in three sessions over the day. I have created drop down menus for participants to choose what presentation or workshop they will be attending over the three sessions.

These are the hurdles I need help with.

When someone goes to fill out the form they must choose at LEAST one presentation to attend over the day. They can attend either 1 presentation & 2 workshops, 2 presentations and 1 workshop or 3 presentations and no workshops.

1. Is there a way to make the form reject a submission if they DO NOT choose at least ONE presentation?? The presentations are the top 3 options in each of the drop down menus.

2. The 4th option (Michael Wilkie) in each drop down menu is an ALL DAY workshop - if someone chooses that, is there a way to then not allow them to choose anything else.

3. The workshops are capped at 25 participants each session. Is there a way to remove a workshop option, once it has been selected by 25 participants in a session, so that it cannot be oversubscribed? If not, are we able to go into the form once it is active and remove the option manually once it reaches 25 participants?

1. Is there a way to make the form reject a submission if they DO NOT choose at least ONE presentation?? The presentations are the top 3 options in each of the drop down menus

You can use conditions to hide the rest of the form or to show a certain message that will let your submitters know that they need to choose those options. For example:

And you can add one more condition that will use the same rules and just show the error message. For example:

2. The 4th option (Michael Wilkie) in each drop down menu is an ALL DAY workshop - if someone chooses that, is there a way to then not allow them to choose anything else.

The same principle like the above, I would use conditions to hide everything else if that option is chosen, but if you mean to choose other options from the same drop-down that will not be possible. So I'm not completely sure how would you like to achieve this?

3. The workshops are capped at 25 participants each session. Is there a way to remove a workshop option, once it has been selected by 25 participants in a session, so that it cannot be oversubscribed? If not, are we able to go into the form once it is active and remove the option manually once it reaches 25 participants?

You can use Disable on submission limit:

And set 25 submissions.

Hope it helps. 

Let us know if we can be of any more assistance.

Thank you!