SharePoint 2016 / sharepoint online

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I have not participated in any projects of that scale, but I can offer some suggestions:

For the documents, I recommend creating a content type for each of those 5, each using a document template (created using Word, Excel, etc.) with the outline/format for the information you'll be putting into it.  If the content types need metadata, create site columns to be added to them instead of making the columns within the content type or within a list/library.  Next I suggest making a document library, adding each of these content types (and storing their document templates somewhere on your site) to it - you could even create those documents in the library but not fill them in yet - and then save that library as a template (to make it available for you to "add an app").  If you're able to make the first site into a site template, it will always have that library with those documents ready for you to fill in.

For creating and configuring the sites...I'm not sure how you would normally do this, but if you wanted to try to automate it using SharePoint Designer workflows, some SharePoint workflow extension tools (such as VirtoSoftware) have actions that allow you to create sites and site collections through SPD workflows.  You may also be able to use workflows to fill out your documents as well.  I'm sure there might be other options that could be faster/easier (maybe PowerShell scripts), but I'm not familiar with how to do that.

For the project as a whole:  stay organized, create a project plan, and constantly reference and update that plan so you can stay on track without any surprises.

Good luck!