Hello. I'm interested.
1. You say no GUI is needed, will serve a CLI command under GNU/Linux? I don't work under Windows nor provide solutions specific for that OS.
2. Are you looking to import into Basecamp all your projects with a single command (batch importing) or you are more interested in a single project importer that can be scripted later for batch processing with Bash or something else? Both can be done, I just want to know the approach to take.
3. Do you have all your projects in a single spreadsheet or you have the information for each project on a separate document? Could you attach me here a sample document?
4. At the end you describe the steps as a very simple repetition of three tasks only. But at the beginning you mention you want to assign milestones and ToDos, so I guess each project may be different and differ in the number of tasks or milestones. Could you clarify this? I need to assess the amount of work to see if my bid is correct.
I prefer to work with CSV if you can afford the conversion. Accessing Excel spreadsheets directly will require another library, while CSV is simpler to tackle. But it's your call.
Thank you.