This sounds like a good candidate for a Service since it is request-based and allows for group permissions to be enforced. You can create a new one in the Service Catalog by clicking the New Service button.
On this page, set the Request Application / Type to Projects for projects to be requested, otherwise this service will cause tickets to be created for the specified Ticketing Platform. This simply determines what is created after the request has been submitted.
It is worth noting that project requests do not support files to be submitted with the request, while ticket requests do. You may want to consider handling these user creation requests with tickets so that the requestors can attach the spreadsheet at the time of creation.
After a Service has been created, you can edit it to control group permissions and associated files by clicking the Edit Service button. Group permissions for the service can be controlled on the Permissions tab for this page. In order to make permissions group-specific, please make sure that Inherit Permissions and Public are unchecked. You can then select the Allow ONLY the associated groups below to use this service option and specify groups as needed.
In addition, you can click the Files tab to attach the .xls spreadsheet to the Service. To allow for this spreadsheet to be uploaded during the request, ensure that a file upload field is present on the service request form. This can be checked by editing the service, locating the Form tab, and ensuring that the Attachment field has been included.
Setting up a Ticket Service seems like the best approach for the functionality you have described. The other approach is to add the file to a Project Template Briefcase, but you do not get the same group permission enforcement.
I hope this helps explain how you can achieve group document accessibility for user creation requests. Please let us know if you would like further explanation or there is anything else we can do for you.