Can I control what each of my staff members is allowed to do on the portal, so a new agent cannot see my cost prices?

Yes, staff work through their own logins and you decide what each login can reach. You set up a separate account for every person in your office rather than sharing one, and then you give that account a role. The role is what controls whether someone can only search and make bookings, or can also cancel, issue refunds, change markups and open the accounts section. A new agent can be given a login that lets them sell and nothing else.

Cost prices are part of this. The buying price that comes from the supplier and the markup you have added sit in the parts of the system meant for you and your senior staff, so a counter agent can be left seeing only the selling price the customer pays. Do check this on your own setup before you hand out logins, because what a role can see is something you configure, and it is easy to leave a permission switched on by accident when you are in a hurry.

Everything a staff member does is stamped with their login, so if a booking is cancelled or a price is changed you can see who did it and when. That also means you should never let two people share one account, or the record stops being useful to you.

When someone leaves, switch their login off rather than deleting it, so their past bookings stay linked to a real name, and take a few minutes to go through your roles now and decide which one each person in your office should sit in.