Allowing users to purchase a "spot" on a group advertising software

I’m working on an interesting design challenge for an online advertising platform, and this part of the project is stumping me.

The basic concept of the current flow is that users can purchase a "spot" as part of a group of people. Then, they can checkout and get to the next step. Here is what the current page looks like:

My idea is to break this into 2 steps: first, the user purchases a spot as part of the group advertisement. Next, they can select an item. This is because the items they will be selecting will be inside of a bigger list, and the dropdown is not a great option for displaying all that information.

My question is regarding the usability of selecting a spot. Some of the spots will already be claimed by other users. Is it correct to show the spots that have been claimed in addition to the available spots? The purchase price is the same for all spots.