So apparently importing is extremely limited into SS, but I do have to maintain historical data from the old site into the new. After some head banging I've come up with the following:
Export data into a spreadsheet or CSV file from old site
Create a SS form with the same columns or close to what I just exported
Let SS create spreadsheet on Google Drive with the fields aligned to the new SS form
Copy the data from the exported CSV file into the SS created, linked spreadsheet making sure the columns and data line up
Now, when new forms are submitted, it'll automatically be added into the linked spreadsheet with the historical data
I can now create pivots, filters or other capabilities to manage the data, both new and historical.
For example: export donors and linked donor donations, by email. New donations with information would be added into the same spreadsheet I just copied data into, I could then create a pivot to report on donations by year, month, etc. that would include historical and new.
Does anyone see issues with this approach before I get too far down this road?